Well I've been absolutely anal about cleaning/keeping everything clean during the rebuild so I don't think there was a bunch of oil on the manifold when I put it back on.

I ran it twice yesterday for 5-10 mins. each time and both times it started smoking after a couple minutes. Then smoke continues to rise from the manifold for a while after I shut it off.

Probably being paranoid about nothing here, but after the amount of time and money I put into the motor I didn't want to ignore it if it shouldn't be happening. Thanks for the feedback guys. I'll post up again after a while with an update.