I use a .040" thick Cometic MLS gasket. Pretty sure it's 4.53" bore.
The KB block has it's own gasket also...may be the same as the BMP, not sure. The steam holes are relocated outward.

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