Buying a spare motor?

After trashing my valves due to my own damn fault I looked around on craigslist and found a 1977 kz1000 motor complete for about $400. Guy says it runs strong and is all original (22k miles). I'm going to take a look at it this weekend. My sense is that it's getting harder to find good spares at good prices for vintage KZ parts and since this is the same year and model as my ride, I'm temped to get it just for spares and upgrading cleaner parts.

Does anyone have advice about preemptively buying spares, or the value that a complete, original, and running 1977 kz1000 motor represents? I'm thinking I could maybe get it for $300 or $350. Would I be stupid to burden myself with more junk or stupid to ignore this opportunity?

Id give $300-350 for a good rebuildable motor that wasnt leaking oil everyplace.
If it still ghas the electric starter on it and oil in the motor Id try bumping the motor over with some jumper cables and run a quickie compression test on it at same time.
Make sure carbs are removed while doing compression test

A good head with no broken fins are whats worth money these days. Maybe up to $200 for a used one.

Cases... $100
Crank $50-$100
Shift Drum $100
Shift forks $100 ($50 each)
Tranny gears / Clutch basket $100
Cylinder $100
Head $100
Starter $50
Stock Cams $50-$100
etc...

See where this is going... Buy it!