[Enginetime]

I've done two 390 to 428 builds. The best 390 blocks are a 66 to 67 date code auto blocks. We found that 3 out of five can be bored to 4.13 (428 standard bore) with plenty of meat to spare. Truck blocks did not pass sonic test as well. The webs may be thicker but the walls were not as thick as the C7 date code auto blocks. Go for the 390 to 428 build up. Far better perfomance, and not that much more $$$.
Mark