I think you are correct about GMS but I never used the tower or gms engines. If you speak with Bill Baxter either at tower or on the factory support you will get a straight answer. When the tower brand came out I was unimpressed with what I saw due to there normal carb problems, air leaks. I stuck with OS until I went to almost all four strokes then I ended up using YS or OS engines.
For two strokes these days I went to the SK but have only used there .91 so have nothing to say about there smaller engines. I have had great luck with the SK and the engine and muffler only costs $100.00. I did have one crank pin break on a new one ut it was repaired and returned in less then two weeks and has been in operation for a couple years now.
These days it can often be cheaper to just buy a new engine then try repairing one if parts are needed. You may get lucky and someone may see your post and have an old parts engine and send you a carb? I have sent several people parts for there MDS engines over the years.