Hello y'all!! This is my first post so I apologize if I break any rules.
I was wondering what mods need to be done to a 12v to make it tow 25k+? It will be paired with built Allision 6 speed and axletech 5000 series axles underneath a 1952 chevy school bus. Thanks for the help!!

 

small compounds and a ton a patients. shoot for low hp 400 or so and big tq over 1000ish. that is a tall asking price for a 12 valve to do well and or often. you need pretty low gears as well. 4.10's or there about. is this 25k before or after the weight of the bus?

 

Should I change anything on bottom end? and 25k includes the bus. The bus weighs about 11k, it will rarely be towing this weight. just towing a camper or my Blazer.