I got a RR upper off the EE that has a FF tube installed. It was special ordered without the swivel stud. I want to put a stud on it so I can mount a harris bipod on it. Do I have to remove the gas block to get the tube off? Is this easy? Would it be hard to tap the alum hanguard to put the swivel stud on. Any advise is appreciated.

You need something like this:

www.mountsplus.com/miva/merchant.mvc?page=MSP/PROD/HARRIS_BIPOD/HBP-ADP-005


Aluminum is too soft to just tap and screw in a stud. This gives you a backplate inside the tube to screw into. I used one of these on my FF HBAR Service Rifle.