What I think I have here is

[FatChance]

Ck filters.... compression test.. I do cold and warm... not more then 10% readings apart. That will give you a idea as to the health of the engine. How many miles indicated ?
Top end job, 2nd over, seals, gaskets... valve job, do'n most of it yourself... $750-1000.oo.. but then it cascades from there.. might as well pull clutch plates.. replace or service... starter spring... rebuild carbs. Remove the points.. toss in magic box....
I'd only do all this and more... if it's going to be a "keeper"....

30K miles on the bike.

 

[FatChance]

Thank you all, following the advice I received here I’ve decided to keep the bike as a runner, not going to tear into the running motor. I’m going to replace/fix, find missing parts, a little late in the year to do much cleaning/polishing.

I see some cheap non running motors on Craigslist. If one pops up nearby maybe I’ll grab it for a winter project in the basement. A practice motor so to speak.

 

[5twins]

I think that's best. I ran mine a couple seasons before tearing into the topend. I sorted the little problems out, upgraded this and that, and determined just what it needed done internally. Mine, like many of these, was in need of a new front cam chain guide. The original was falling apart, as I discovered once I removed it .....

Yes, if the 650 bug bites hard, as it has for many of us, a parts motor, or better yet a whole parts bike, is a wonderful thing to latch onto. Checking individual used parts prices on eBay will show you what a deal this can be.