I agree that a 750 would be the largest carb for it. The 383's I've messed with did not like big carbs like a 440 does. I had a mild 383 w/ big valve 906s, 9.5:1 compression, MP 484/284 cam...it ran WAYYY better w/ a 750 than it did when I tried my 830 holley DP on it.

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