I have an M16 with a hinged floor plate now being rebarreled, T&T and restocked by Sharp Shooters Supply. I'd like to keep the HFP configuration but I understand it can be converted to a DBM with new bottom metal and a magazine bottom plate and that these parts fit the stock exactly the same way as the HFP. Is that correct?

So, it is feasible to have both magazine types in one rifle? That is could I buy the DBM parts and switch the rifle from HFP to DBM and back at will? Any idea of the cost of the extra parts?