I towed with my 85 w150 318 4spd, she had header's, 4bbl intake, duel exhaust but she was tired
so I think the tiredness canceled out the aftermarket part's haha but she would haul damn near any thing 323 gear's she would do 65-70 down the highway with a car trailer on it an a full size 85 suburban.. a buddy has a 92 dodge 3/4 ton 360 auto
but it has hauled his 5 wheel + a trailer behind that Pluss the box full of stuff an cab full, trailer full, camper plum full lol to Portland an back 2-3 time's an has yet to give him ANY problem's.. maybe im crazy but I like a manuel to tow with, you can chose your gear's ya want but like every 1 say's look for a cumin's you maybe a 91-93 5spd w250 318-360