For what its worth, if a good 305 is available, and for the application you described, I think the 305 would be fine.

If you have to overhaul it, it will cost exactly the same to overhaul a 350, so the 350 crate motor looks like a better bet.

I had a '77 Nova with a 305. It had great torque and outstanding gas mileage. I had one of the early ones with soft camshafts, and I replaced it with an Engle RV cam. It helped the gas mileage but really hurt the torque (it lost over a second in the quarter mile!).

I wouldn't worry about pulling a 4000 lb or so trailer with a 305 - you'll be fine.

---> Bill