GM Vortec Crate Engine Differences

I'm looking to put a replacement style GM truck engine in my '64 C10. Specifically, I am looking at their L31 type engines originally found in '96-00 Chevy full size trucks.

Does anyone know what the differences are between GM #12530282 and #12530283? They seem to be identical EXCEPT that #12530283 has 4-bolt mains. Are there any other differences? #12530282 is designated for 1/2 ton trucks while #12530283 is listed for 3/4 and 1 ton trucks with the "heavy duty option". This is all according to Pace Performance. Can't decide which to go with if the 4-bolt mains is the only difference. Hell, its only $40 more... but I wanna check with you guys first!

#12530282
GM Goodwrench - 12530282 - 5.7L (L31-R) 1996-2000 Chevy/GMC Full Size Trucks, 1996-2002 "G" Van, Savannah,Express Vans - Under 8,600 GVW

#12530283
GM Goodwrench - 12530283 - 5.7L (L31-R) 1996-2000 Chevy/GMC Full Size Trucks, 1996-2002 "G" Van, Savannah,Express Vans 1996-1999 "P" Vans- Over 8,600 GVW 96-00 CK2,3 G (L31) 99 P3 (5.7R) CPI HD