The Poulan 42 and 46cc engines come out of chain saws. As you said, the 46cc engine needs to have an intake manifold made, but it is the better engine. More power and a good bit lighter as well. The 42cc engine is ok, but does weigh more, and you must convert it to electronic ignition. The coil for the magneto ignition mounts in the saw; not on the engine for the 42cc. So you can't use the factory magneto on the 42cc.

AV8TOR