Keith,
I have seen pictures of Ray's 1720T. I think it was his go to gun for certain travel restrictions.
Way back when, Marmot Militia made me a long tube for Prod, but that and follow on company, WAR, is gone.
Being you are building a rifle, using a Fortitude air tube can be an option. There would be a few different ways to go. It is about 9 1/2" longer than Prod/1720T air tube, which works well with a shrouded 20" barrel.
Would you happen to know if the pistol trigger group will bolt up to it or is there some work needed to make it work? Also do you know if they are both the same diameter tubes? If so that would help in being able to use some upgraded parts for the marauder.
The pistol trigger assembly, should bolt up and work, but I have never tried it on the Fortitude tube. I did try it on that MM tube, for a very short time, but found it very awkward. On converting to the longer tube, stocked rifle, have always used the Mrod Gen 1 trigger assy. It is better, and especially if you are looking at a competition rifle.
The Prod, 1720T, 1701P, Fortitude, Maximus, and Disco all use the same diameter tube. What can actually bolt up or easily modified to do so, is model dependant.