If the mag housing is metal and totally encloses the mag it has been converted to the metal ( pot metal) mag. The back of the plastic mags slide up a spine of metal and were locked in place some how. A mag housing off of a model 64B will fit and conversions are around which will allow the Metal Cooey 64B, the Lakefield 64B, and now thw Savage 64 model, mags to fit( sometimes with a little filing because it is 3 different manufacturers and maybe 50 years of different products. Put a "WANT TO BUY" on the "equipment exchange" for a "COOEY MODEL 64B MAG HOUSING AND/OR MAGS IF POSSIBLE" see what happens. To replace you remove the stock then remove 3or4 screws substitute the new part and reassemble.