If you can get her running without tearing her apart, why not? But I wouldn't chance actually taking her out until you at least split the crankcase just to see how the transmission, clutch, shift drum etc are doing. You don't even need to remove the top-end to split the crankcase!
I explained to your dad that it's likely going to have some sludge at the bottom. Sure you can pump diesel through it, but it's much faster to thoroughly spray some B12 Chemtool in the bottom crank case and of course you need to check on the aforementioned parts!
If she's turning over, congrats! That's a good hand to be dealt. Now hurry up and check compression! If those valves are sealing you have a great top-end to work with without even needing to rebuild it just yet.
The bike your dad gifted us boys over here was locked up pretty tight. I stuck an air-compressor hose into the spark-plug hole and she turned great! Wanna race? By that I mean see who gets it running first! Haha.