There have been some interesting posts about using the 4.15" Crankshaft in the 383. Using the Short 383 Rod may not be feasible, but you could use the Long 440 Rod.
Why do you say that? A 1.12" CH seems unfeasible to me.
A 4.15" crank in a 383 or 400, what's the diff? I've heard of many folks installing 4.15" cranks in 400s (MP makes a crank for such an application.
I haven't heard of any extensive mods req'd to get a 4.15" arm in a 400. 383's the same deck height so it should work w/a 383; just need to find pistons for it.
