Having modified three DPs to use the RP belt feed, there is more involved than just assembling the top cover. The RPs were improved DPMs, having a heavy barrel with a much larger and sturdier gas block with a larger adjustable regulator and ports, a lever operated barrel change thru bolt, top mounted bipod attachment to the shroud and a number of other improvements to the DPMs. DPMs have the recoil spring at the back of the receiver to protect the recoil spring from overheating.
While the belt feed mechanism appears to be a simple task to repro, it is really not. I know of several guys who set out to make repros, but the project was more than they wanted to engage. Cost would be high with a limited market. Relatively minor mods to a DP or DPM are required on the shroud, rear sight and gas ports to correctly assemble the RP beltfeed.
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