I wasn't aware that the R blocks were allowed so yeah they will take up to a 4.22" Siamese bore with a 4.25" crank that's about 475 cubes.

So with a lightened block and 48 degree lifters and 13.5:1 I can see it being fun figuring out how to go 10's in an A body.

The biggest 'trick' is with a restricted exhaust you have to figure out how to the intake to feed the cylinders adequately all alone (without the benefit of overlap) so wide centers and big (in a SBM ) 2.15" / 1.56" valves.

With high compression and good combustion, surprisingly, the exhaust can still get out of there very quickly.

Also I learned a long time ago that under the right conditions a big motor can pull through a 'too small' port and effectively toss the 28" flow numbers right out the window in terms of HP/CFM

I might get back interested in this class again.