Most 4.25 cranks have a minimum rod length listed in the catalog. Double check to see what the mfg says. I'd use a 7.10 rod in an RB block but I have used 6.535 chevy rods in low deck engines. Also, if you haven't verified the deck height of the block then don't assume that it meets factory specs or that it will clean up at factory specs. Most Mopar blocks need to be cut a bunch to square them up.
The crank counterweights will have to be cam cut a LOT to clear at BDC. Add mallory metal to balance it and its not worth it.
