Well, the marine stuff is out, not only after 1project2many's comments, but my research. The 302 idea would work if I saw high rpm's, however using my handy dandy self made excel spreadsheet, with my 3.73 gears, 700R4 and 265/70/15 tires, at 2350 rpm in 3rd gear I am doing 55.5 mph, 80 in overdrive (not that I would tow in OD). if it kicks down to second, 3500 rpm is 51 mph. I need torque in that kind of range. The 406 was a torque monster on DD, but I give up a lot when I switch back to a standard flat tappet cam. The trailer loaded is going to be somewhere just under 5000 lbs. loaded, so I will need lots of torque. I guess my real question is with the 350, I get about 415 #/ft of torque from 2000 to 4000 rpm. Will that work? The 383 gives me 450 #/ft of torque from 2000 to 3500 rpm. obviously this is DD, so results may vary. My question is mainly if I have over 400 #ft of torque at the flywheel, will it do the job towing? BTW, thanks everybody for chiming in, I really appreciate talking to people that aren't trying to sell me something but have real world experience with the kind of motor I am interested in building.