To make older (NICE and guide light) bags work on an MT frame, You would need a buckle adaptor set (or buckles) which is about $20. Called the time machine and MR sells them from their repairs department. Same thing to make new (MT) bags work on an older frame. You can brew your own if you like.
NOTE - I am a bit of an MR fanboy and have owned several packs and frames going back to 1997. I am also selling two MT frames in the classifieds so my comments are a bit self serving. So…
My $0.02 The guide light was fine. Lighter and better than the NICE frames With built in load lifters. My only real issue was the hip belt slipped. The guide light MT is better IMO. More refined. Lighter. More padding in the belt and a better belt design. the MT wasn’t a full scale revision but it was a nice refinement of the guide Light. Unless I got a screaming deal on the guidelight, I wouldn’t buy one because then you have to factor in the cost and pain in the ass of adaptors going forward. I would also stay away from nice frames. built or overbuilt for military specs. They are great. I still keep one as a shit hit the fan pack and one for training but they are #2 heavier than an MT and you really need to add load lifters to get them to carry well IMO, which is another $50, more weight and harder to find these days.