So just an update...I ended up going to Tactical Ordnance (amazing outfit) and Casey put on an RMR mount (TacOrd one, which was more than I needed - didn't need more expensive ones) for my newly acquired 507c x2 (which I later realized it would have been cheaper to buy the red dot directly from him as opposed to my local retailer), mounted it and I also got a Nordic Components mag tube extension, which he put on for me as well along with barrel clamp and gasket (add-on). I also got a rear half ring aperture to co-witness. Everything looks great and he did a great job while I waited.
It is interesting - I was talking with him about the mag tube plug. So the front of the tube is flush with the end of the barrel, but there is an aluminum rod that is permanently on the NC end cap. That conforms to the legal limit. He actually said TacOrd supplies other retailers so they would be better the same thing. If a retailer sold the kit without having a permanent plug, the buyer may unknowingly be installing something that puts them over the mag tube limit (which appears to be 5 x 3" shells, and I guess before 5.9 shells of 2.75" could fit, but now it is 6 shells in the tube for 2.75" but the 3" shells is still max 5).
Anyways, the barrel clamp has a short picatinny section for which I can hang a light. I was hoping I can swing a tape switch with the light but there is nowhere to secure it, unless I zip tie it directly to the handguard, which will look uggggggly... I want to be able to turn the light on and off with finger or thumb, while my two hands are holding the handguard and stock respectively. It is really too bad this version didn't have the MLOK handguard - that would have allowed both the placement of the light and tape switch in an optimal position.