I'd go w/ the 4.25" stroke.
Seems there was a discussion a while back by one of the big name builders...like Kaase or maybe Reher-Morrison, I cant remember who exactly. They basically said the rod-stroke ratio didn't really matter when it came to making power.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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