the 590 purple or something similar .
557 could be all the head would make use of.
it takes good heads and a big cam to make power with a 440 @ 6500.
6500 would be a good shift point with the right cam.
The thing about an RB engine is you don't need to spin it to the moon to make good power. I prefer to keep the R's at 6K or below. With the longer stroke, just think how fast that piston is moving & the stress. Just my opinion, of course!
