What we think is largely dependent on the condition and current state of the build. I definitely would NOT consider this as a grab and go toy. It looks like it's going to need quite a bit of work.
The fact that it doesn't have an expansion chamber is a huge testament of the builder. I'd be going through an extremely thorough check of this bike. The order of the things that I checked would be the same order that I did to build the bike.
Frame modification and weld quality
Engine mounts and weld quality
sprocket alignment and chain clearance
In your case, axle housing mods and brake mounting
Pipe fitment
carb clearance
Airbox and tract routing
Clutch, brake, throttle routing and function
Electrical
THEN, you can get into the quality of the engine.
If you do go look at it, I'd recommend getting a phone number from a member here so that you can have someone as a consult as you check it out. If you want, PM me and I'll do it. There are a handful of others, but I won't volunteer their names.