All I was told when I bought this car (66GTA conv) was that it was an early 60s Tbird motor as the original mill had been blown up. When I rebuilt the engine the heads were 406 6V heads (427LR). I cannot figure out the block.
It should be a 390 block by the casting number. 63 was one of the last years some casting numbers "made sense" and were not as generic. If you rebuilt the engine what pistons, rods and crank did you use? That would be a clue no?