Can I safely turn down the 4.6 crankshaft from 2.185 down to 2.100 so I can use Chevy rods?
Shouldn't be a problem, some builders on V8Buick have been offset grinding the 2" journals on the SBB 350 to 1.880 or thereabouts (Toyota and/or Honda journal size) to gain more displacement. I did similar with ex-Nascar rods (Carillo and Pankel) for the 300 stroker motors I've built but without the offset. Can't report on the track record of those engines yet but have heard of no reported failures so far. Those are high nickel sintered iron cranks, not forged. I've run the standard 340 crank to 7K with no issues but that was with 7" Scat rods and Venolia pistons. So YMMV but I certainly wouldn't be scared to try the 2.1" journal. Can't see that being inadequate.
Jim