Every piston gun is different. It's not Kalashnikov simple, where you can cannibalize one together. If parts break, you'll have to go back to X manufacturer to get said parts. DI has yet to fail me while in some bad situations in Iraq, so I wouldn't bother. Word on the street also is the gas block. The piston actually strains the bolt during unlock as well. Someone tried to reinvent the wheel with the piston operation. It was a fix to a problem that never existed. Failure of the AR/M16 direct impingement has never been the gas system.
In short, as one has already said, don't waste the money on the conversion, just buy an out of the box piston AR if you really want one.