What gauge spokes? 12 or 11 ? a heavy duty spoke is best for a motorized bike considering all the weight of the bike in it's entirety , road, riding conditions and vibration that the wheels will absorb.
But I'd be going for a bigger one than the 49cc.
Then It might be sitting pretty high in that frame, and be heavy.
I have no experience with the pred' motors in bikes, but there's some nice builds on here.
I'd go with a Hue sheng 49cc kit since you seem to know yer way around welding and mechanical you could modify just anything to fit yer needs/desires and the motor is very Torque'y , I have never weighed any of my bikes as a whole but over all they don't weigh excessively much and the weight of the engine should be mentioned in the kit specs + weight of the bike.
Some new pics with the new wheels. Must say it looks the bomb.
Still deciding on the engine. This is just way to hard. Over all I am mega happy with the whole outcome of the ride.