He's got complete mechboxes..."nice" ones like the King Arms...and "ok" ones like Action. He's also got just the shell and every individual part to go in it.
Re. fixing your ak/v3...while it may seem cheaper to just buy the shell and try to move all your parts over, it can be a real pain in the a$$ sometimes. Sometimes it's a snap and it all goes smooth the first time...other times you just feel like junking the whole thing it's so frustrating.
Which ever route you go...
- try not to mix and mash different makes/brands of parts within the mechbox/shell. As "standard" as they are...there's lots of differences.
- it's nice to eventually end up with a spare mechbox that you know runs...then when you have issues down the road, you aren't all stressed out about getting your gun up and running. Also...you can fiddle with the spare mechbox to figure out how to shim/setup different parts without taking down your gun. If you like models/mechancial type things...you might really like messing around with mechboxes.
- avoid bottom-barrel parts...they tend to be off-spec and hit-miss. Some parts might work fine...others might look ok, but not work in your setup. In general...a waste of money/time.
Re. your DSR...you're going to have to do a lot of research and fiddling.