Max Torque Big Block

If you crank the performance up, definitely going to have to upgrade the cooling too. Also, since no one has asked the question... Does it have the industrial medium duty413/440 with the commercial municipal water pump and the gear driven reverse rotation cam or is it a standard 440 truck engine? I mentioned Cummins 5.9 litter first, but I think the best upgrade would be an IH DT466 with a six or seven speed Rockwell from a medium duty International truck. All kinds of those on the market in municipal or utility auctions. Rest of the trucks are worn slap out but the powertrains are slant 6 reliable.