https://www.ebay.com/itm/115527150035?
pretty close to the discount $499 for the moto cult kit wouldn't you say.
Tinkering is still tinkering...but for the money I think I'd go a whole new engine.
There is pretty good chance the wiring will be plug to plug, if not shouldn't be hard to snip and crimp a solution.
The 5 speed 172fmm-3 non balanced engine is a bit cheaper but should be a direct bolt in swap for all CG/CB frame types.
My XL185 frame took a cg250 and a cb250 no issue with lower mounts...
on paper a standard cg250 is 10kw/14nm. the 172fmm-5 claims 14kw/18nm. So I would say there is a difference in power and torque.