[Bruce Edwards]

Build you own. You will have a better idea of what you have and if something does go wrong you will have the knowledge to repair it.
The older engines are not hard to build. One thing you will want to do is get a good machine shop to do the machine work. Your friend should have a machine shop he uses and trust.
Do some reading and figure out what you want the engine to do for you.
You will be a lot happier with it if you build it the way you want it.