Mel

Is the switch possibly stuck internally? Hopefully, you can disconnect the switch, put an ohmmeter on it and work the shifter. Good luck.

Regarding the tires: Do you know how old they are? Not sure about tires sold in Europe but tires sold in the U.S. have a date code stamped on the side wall which is oriented inward -- i.e., crawl under the car to see the code. In U.S., a four digit code of 3217 will be the 32nd week of 2017, 4319 will be the 43rd week of 2019, etc. Good luck with the 'new' Avanti and come to the forums often; lots of good info and input from many longtime owners.

Some of the aftermarket gaskets are a bit thicker than the OEM's and thus the manifold sits a bit higher. Bottom line, don't put a thin bead of RTV on the front and rear 'china walls'; use a good thick bead or you'll end up with an oil leak. And, use brake cleaner to be sure all surfaces are clean of all oil and grease. How do I know? Experience.

My '66 has the 327/300 motor. The number on the intake manifold immediately behind the carburetor is 3872783; immediately under that is GM2. The number immediately in front of the distributor is J185. The carburetor is a Holley 4160. I don't believe the 327 was still manufactured in '78. GM was making the 350 by this time; perhaps Avanti Motors bought a bunch some years earlier and was still using them in '78 -- I don't know. The 327/300 had 2 'humps' on the front of the cylinder heads, one on each side; they were called 'Camel Hump' heads. Hope this helps. Good luck.

Rear brake: shoes, (original setup), hoses, wheel cylinders; U-joints; heater and radiator hose... Good luck.

An idea for you Zedman: If your interior is apart, when you put it back together, you might want to put in some heat insulation. I bought some adhesive backed insulation and put it under all the carpeting, seat bottoms, back panel, etc. Seemed to help keep the temperature down inside. Good luck.

Wide fluctuation sounds to me like a bad ground. The first thing I'd try is running a separate ground to the gauge 'casing'. There are two main wires leading to the gauge, one from the ignition and the other from the tank sending unit. Good luck.

My car is in the body shop, thank you insane driver in front of me, and I haven't stuck my head that far under the dash lately. But, as I recall, you can remove the pin which attaches the brake plunger to the pedal arm and loop a tie, of some sort, to the firewall area. This gives a bit of headroom and arm room. Good luck.

On my '66, the relay is box-shaped and has a three pronged plug which, when viewed from the top or bottom is triangular shaped. Mine was intermittent and fixed by pulling the plug, spraying some contact cleaner in the prong holes, sanding the prongs and bending them slightly so as to have a snug fit. I then put a zip tie around it to make sure it stayed in place. No problems the last 15 years. Good luck.

Make sure your emergency flasher circuit is not stuck in the 'ON' position, the switch is well grounded, etc. In these fiberglass bodied cars, bad grounds cause all kinds of problems and the more grounds you have the better. Welcome to the world of fixing things that others probably screwed up. Good luck and keep us posted.

The oil pressure gauge and speedometer hookups are the two I'd look at closely before proceeding. Keep us posted.

A few thoughts: My 66 had the original B/W auto trans. which I had swapped out for a 700R4. As I understand it, that transmission was made for the 'B' body (big) GM cars -- Caprice, etc., (which were a lot heavier than an Avanti) and were electronically controlled. A couple of kits were installed to adapt it to throttle (only) control. The shift from 1st to 2nd is of higher RPM, probably to get a Caprice (tank) moving, than is required for the Avanti and the shift is 'solid' if accelerating slowly but smooth if accelerating hard. I've not tried adjusting the throttle adjustment but a GM guru I ran into was not surprised. It may just be the nature of the beast with the throttle control. I don't like to dog it so the 1st to 2nd shift gets a little annoying. I've not had any experience with a 350 but the above is something I'd keep in mind. But if you are going the distance to do an engine swap, I'd definitely think GM transmission. An overdrive drop the rpm to ~2150-2200 at 70mph and lets you hear the person sitting next to you. Regarding the cam and lifter wear. I was not familiar with these sbc motors being notorious for having this trouble but these flat tappet cam engines need zinc. You can read up on this but, as I understand it, zinc molecules in the oil create a microscopic clearance between the lifter to cam lobe and the rod bearing to crank journal surfaces. You can buy ZDDP additive but Valvoline VR1 Racing Oil and Shell Rotella fit this bill. The parts stores often have to order this from their warehouse. Good luck.

Take the rotor off and clean all the grease out of the areas, inside the rotor hub, where the bearings rest and see if one of the beveled rings (race) inside seems loose or can be wiggled around at all. You stated above that you repacked the bearings but if you ascertain the existing races are pressed in tightly, I'd consider having the races replaced and install new bearings. Did the noise start suddenly after you did any previous work, hit a pothole, etc.? Is it particularly prominent during a right or left turn? Sounds to me like a bearing/race issue. Good luck. Keep us posted. Thanks.

On one car I had, eons ago, one of the bearing races was a bit loose in the drum. The bearing had never seized so I don't know why the race was loose but ... Might be worth a look. Good luck.

It looks like the car is basically all there. You have to decide how much you can do yourself and how much you are willing to spend. Personally, I have about twice invested in my car than I'll ever get back, all the (extensive) labor on my part being free; I don't regret a single penny spent. These cars are an absolute joy to drive and always get great comments. Good luck!