cocking tube and support will be k length. Support you will actually have to check, it may need to be custom. DISCLAIMER: I have not built a reverse stretch yet, so am just referring to what I have read and my 51k build experience.
Bolt carrier should be regular, a k will fit in there but with a full size reciever you have room to run a full MP5 Bolt carrier. You will have to see about what locking peice you may need to properly cycle it though.