Is that stud girdle as light as it looks? I have a 1983 4.2 with 4.0 head & EFI. Could I just stick a factory stud girdle into my block or is there a difference in the main caps or something else that would be a problem?
That girdle is actually pretty darn stout. IIRC, it's over a 1/4" thick and has quite a bit of heft.
If I were you, I'd take that 4.2 crank and drop it in a late block (they're a dime a dozen at the bone yard) and make yourself a 4.6 stroker. :) The main cap bolts for the girdle are different and do interchange among the 4.0's but I don't know about the 4.2's. Oil pan clearancing my be necessary too.
