[rritchey]

Excaliber,

I know it is not that big a deal to tap the freeze plug holes and put in threaded plugs. It is also relatively easy to tap and thread a 390 or 406 block to accept the cross bolted caps (so long as the block has the bosses). I've done both of those procedures to blocks for customers who requested it (so their blocks would look like a 427). I just don't know of any 427 blocks that did not have a pressure relief valve in the rear of the block either at the rear cam plug (center oiler) or in the lower left hand corner (side oiler).