This seems like a fun thread, haha. Might need to just rock the bike in gear after a lot of heating. Assuming the rear wheel and chain are still on. I bet inside the motor is clean though. My 650 was in rough shape too, good thing I only needed the motor. I did break a few case and head bolts getting it apart.
Regarding the carbs, the 750 carbs won’t work. Thats only for the earlier 650 which has different head manifold spacing. I wouldn’t be surprised if you could find a good rebuildable set of the VB’s on eBay.
What’s the ultimate goal for this bike? Stock? Cafe? Weekend track bike? If the latter you might want to consider CR26’s instead of messing with the cv carbs.
If you want, have a look at the build thread link in my signature. I’ve got a 650/674cc motor in a 550 frame with other fun upgrades. I really like the SOHC4 650 motor.