Jack, it sound like you are describing my '76. It still has the original 400 block, crank and oil pan. Motor was first rebuilt in '11 and equipped with a hydraulic roller cam, head work, new aluminum intake and carb putting out 360 hp over the original 175. Two years ago, as motor was undergoing conversion to TBI fuel injection, a cracked head was discovered and it had another tear down, new pistons, rods, cam and aluminum heads were added. Motor is running nicely now, putting out 470 hp and 570 torque. A 200R4 was added in 2011 as well, making it a nice highway cruiser that can more than keep up with today's traffic. I'm thankful it does not have a sunroof. I was impressed with the overall quality of the car as I had a '64 years ago and the Avanti II's body quality, build quality and interior are superior to what the '64 had.
I also have an '89 convertible that I bought 5 years ago already resto-modded with a 383 crate motor and a 4L60E trans with a Ford 9" rear end. The steering and handling of the '89(Caprice suspension) is superior to the '76 with basically the old Studebaker suspension. For long range traveling, I prefer the '76 being quieter and more comfortable than the '89. A spare and spare cover in the '89 takes up all the trunk space. The Lamborghini Red color with black interior and black out trim makes the '89 a drop dead great looking car driving around in the summer with the top down!