A 400 block would be able to go 4.185 with a decent sonic test. A 4 inch stroke can go in one with honda rod journals and small base circle cam. May be able to get a hair more stroke by measreing every thing real close, bore may get a hair bigger with a sleeve or hard block. As you can probably imagine the rod/stroke ratio is nice at that long of a stroke.

I think in the spirit of the rules a 400 block should not be allowed same as a 340 resto block, but in the strict technical interpritation of the rules they are ok.