R3 Header question

[Avanti1963!]

I have what I think is a pair of unused R3 headers.  Three pictures are attached.  Please help to answer a few questions. 

-The left and right look exactly the same. 

-These don't have the alternator bracket sticking out of the front of the passenger side. 

-There is a part number 1558353 cast on the right horizontal face on each.   On the other front face is cast 206-86. 

-Pictures of the reproductions don't seem to have a number.

What do I have?  What models do these fit?  

Thanks

Edited 2 hours ago by Avanti1963!

[mfg]

Not sure, but I’d guess you own the real McCoy… Amazing how, after all these years, rare parts like these still turn up !