A500 or A518?

An adapter from small block to big block doesn't work very well. The small block starter location is lower and interferes with the block casting protrusion for the drivers side lower trans bolt. Any adapter would require you to saw off part of the block. It might not hurt anything and i think somebody has made these adapters, but ive never seen one.

A better way is to saw off the bellhousing from the trans and use an aftermarket one like a J and W that bolts on via the pump bolts. Im not sure if they make one for the A500 or not, but they do for the 518. I have set up a 518 for a big block this way and it works. The A500 or 42rh uses the same pump bolt pattern as the 904, just like the 518 uses the same pump bolt pattern as the 727.