Hello Andrew,
If your engine number is indeed CB750E-1001086, that is within the sandcast range. To check if the cases are true sandcast, and not restamped diecast, count the number of bolt holes for the clutch cover. 9 holes means sandcast cases, and 10 holes means diecast.
Pictures help us with offering opinions of value, and restoration worthiness. I can say, some people start with just a frame, or a motor and build from there. Any sandcast is worth trying to save, in my opinion.
Cheers!
Gregg