nearly complete  MOD 0..waiting on bolt and barrel.
I still have a few small items to get and need some advise on
which parts are correct for this rifle.
only parts left to get are gas tube, buffer and buffer spring and
these are the items i'm unsure of what length spring and what
waight buffer and finally what gas tube like standard or fatboy
ect.
I have RRA upper and lower, PRI Gen II carbon fiber tube
WOA SPR barrel soon and crane clone sopmod buttstock no
spring or buffer. just needing to be sure on the gas tube spring
and buffer for correct cycling. stock will most likely always be  
fully extended.
thanks guys.

anyone have an answer on this?

I think everyone is getting a little tired of answering post like these.  I have one very similar asking how to finish a Wilson Combat upper.

Someone here must have something to offer...

Are you asking what length gas tube?
There are only really 3.
CAR/M4/Midlength, and Full Rifle length
They all work very well.
No need for fatboy, etc...
What barrel do you have without the abbreviation?  Link?