Personally:
Best Cylinder : 2F4R 47.6mm Bore with 44mm Stroke =78cc
Best Carb: Genuine Keihin PWK 28-33mm Carb
Best Ignition: PVL Digital Programmable Ignition
Can you modify your existing crankshaft : dont even think about it. Gives you more Headace.
To save money is to buy the right parts the first time!
Goodluck on your project