I'm assuming it's a Chevy TH400...To swap the motor in, you need to find a bellhousing from a BOP (buick, olds, pontiac) car with a TH400. The bellhousing bolt pattern is different. I *think* you can get a plate that will change the bolt pattern from different people, but I'm not sure. The motor you have has 150HP/245lb-ft from the factory, so it might not be the best engine if you've got a big truck with steep (numerically lower) gears. Well, then again, it'll move my 3800 lb delta 88 with 600 lbs of stuff in the back end at 80 mph on the highway with 2.73's and a .67 OD gear ratio in the tranny, so it shouldn't be too bad...
PLease refer to the website
www.realoldspower.com for more information about olds motors in general and maybe some ideas on how to put that in there. Also, check out the post in Hardcore Race Tech about Bill Trovato Racing's engine getting the #10 spot in the PHR Engine Master's Challenge. We're pretty proud of that.