There were 3 different 'versions' of recoil plates over the years IIRC. Slightly different design angles to help improve the fit between the recoil plate and the receiver. A good tight fit here is essential to a carbines accuracy. It isn't absolutely necessary to have an IBM recoil plate mated to an IBM receiver. However by the time IBM started producing rifles they were built using the final version (tightest fit) of the recoil plate, and would be most correct (historically) for your rifle.
The recoil plate should be a snug fit to the receiver (out of the stock) and should require moderated thumb pressure to get the bottom of the plate to touch the receiver. Ideally, the lower tab should wedge itself into the receiver and hold the recoil plate in place. If the tab touches the receiver under it's own weight - it's too loose. If it does, the above .pdf describes a method of working the recoil plate for a tighter fit.
Your other option would be to try to obtain a number of recoil plates and trial fit each one to find a better fit. Be aware that any unmarked recoil plates are either of the earlier types, or a cast aftermarket part and should be avoided. (The cast ones.)
Last edited by Highpower; 01-21-2010 at 02:51 PM.