Those Pontiac engines are HEAVY and WIDE! You're almost certain to encounter steering gear clearance problems, and the springs will have to be beefed up considerably to hold up the weight.
How about the Cadillac 472 or 500 engine? I towed trailers all over the country with a 70 Caddy Fleetwood Brougham, with a 472 and a Turbo 400, with no problems whatsoever, even when the engine had over 200,000 miles on it, and I towed a 10,000 Lb. trailer from California to Tennessee. It's certainly got the torque! Surprisingly, it doesn't weigh much more than a smallblock Chevy engine. There are several items of dress-up and speed equipment out for that engine, headers, manifolds, roller rockers, etc., but box stock is still pretty impressive. I've got a 500 with a 400 trans I'm planning to graft into a 59 Suburban one of these days.
Jerry
