It can be a challenge especially with the spark plug but the Chinese 2 stroke kits can be very successfully installed in a 24 inch frame. There are shorty plugs available if that becomes an issue. Frame to chain clearance can also be a problem but with a little ingenuity it can be overcome. You'll want to stay with a smaller rear sprocket, maybe a 36 or 41 T. Here's one I did. http://motorbicycling.com/f15/2door-uncle-santa-14211.html Good luck.
Tom
Thats a nice looking bike. I was thinking more about the pre and post war cruisers. Im not planning anything else right now I have my hands full with http://motorbicycling.com/f41/jenny-irene-so-far-20211.html but a guy across town has a couple for sale I was thinking of picking one up for a later project.
the frame, fork, bars, stem,chainguard, front fender, cranks, sprocket and chain are all original parts. wheels are older Worksman with a Bendix rear hub and an Atom front drum, Brooks seat, and a backwards motor.
We have seen quite a few in-frame motorized 20 inch wheeled muscle bikes on this site, so a frame for 24 inch wheels should be no bother (I've been reading too many Intrepid Wheelwoman posts).