Re: are there different 'types' of 390 block?
More than likely your 390 from the T-bird is just a stock 390 300hp. The 390 from the truck will probably be a better, more stout block, because it is comming out of a truck. Check the sides of the block for long rectagular ribs, if it does than I would use that block, it might even have the extra webbing at the main caps...(MIGHT) that would be a plus. The bores on the engines should both be 4.050 in. The truck blocks' pistons more than likely have a long skirt on them and maybe a different wrist pin location, if you can get away with honing the the truck block cylinders and use your original pistons and rods, you might just get away cheep.