PX 200 engine to 1962 vespa 150 (vbb)

I want to put new/bigger engine to my old vespa. Idea is to build superb vespa for longdistance cruising, cruising speed about 100-110khm. Many people told me here that it needs a lot modification to fit px200 engine to my old vbb frame, is it really so? I can not see any problems. If you do know some, please share this info!

I can only think one problem, wiring. Wich wiring harness i should buy (from SIP) for my project. Tell me? I dont know much about the engine, I  bought it from ebay, its a px200/lusso, kickstarter model. Thanks