I like to call these stovebolts "glorified tractor engines". They were designed and built to have lots of low end and midrange torque, and the bigger manifold runners and ports do little or nothing to enhance that. They do have somewhat better top end horsepower, but for the vast majority of the speeds a working engine is going to run, you need torque, not horsepower to move the load along. I'd definitely use the original manifolds, even if an adapter is necessary for a proper fit.
If I ever manage to get my dyno back up and working, maybe I can do some documented testing instead of making a SWAG about some of these discussions!
Jerry
