I'm not very familiar with the RFVC engines, other than having a basket case xr500 pass through my shop while I was transporting it for a buddy. I did end up looing it over pretty good hoping to "borrow" a few parts for my non RFVC 500 before discovering that there is zero parts interchaingability.
But I do know that on an older single you are very likely to have some valve spring collapse. It dosen't cost anything to pull the valves and measue the valve springs, and stock springs are pretty cheap, way cheaper that risking floating the valves till they interfere with the piston. If you have a top end gasket kit it likely has valve stem seals and pulling the valves will then let you install the new seals.
I think your idea of trying to get it runing before spending much on it is sound, but once it is running how likely are you to pul it apart if you hear something? or would you be tempted to run it into the ground? I know how tempting it is to just ride a cheap dirt bike till it dies.