Willyb, its a oil bypass plate for a LS6 engine. It provides clearance for the shift linkage in the FFR GTM Im building.
The spindle problem can be one of two things. One has been solved with a heatsink on the vfd controller. (mine came installed). On faster computers, if you dont set your voltage on the vfd while under computer control, it will run the spindle out of the speced RPM range and shut down. Simply adjusting the voltage as outlined in the manual will take care of it.
Im guessing what you hear in vibration, is harmonics of the stand and its associated sheetmetal. It will act as a speaker and amplify any noise the machine makes while cutting. I havent heard anything to be concerned about.
You mention converting a mill to cnc here:
http://www.cnczone.com/forums/showthread.php?t=27574
Are you converting a mill and buying one also?
David