I have a SN-60 paxton on my 57 312 that had not been run since the 70s. It worked well on my first few shake down runs up to 5500 rpms  then 2 7000 runs and back to the pits it felt warm not hot. Now I try to spin it after a few months and spins very hard is 7000 to much and if so is there a fix I plan to rebuild it so if there's a fix now is the time1