1) - the RPD is not 14/1 L threading. That being said, I am having mine built by Stan at Project Guns and he is turning the threads to that for me.

2) - tripod.... I'm guessing you mean something like this :




I'd get the quad rails from DSA and then do a custom mount to a tripod. Or you can get one of the saddle tripod mounts and just clamp it around the factory front handguard..
http://soldiersystems.net/2012/01/17/hog-saddle-tripod-mounted-rifle-rest-improvements/