Thank you for all the efforts vascoribeiro, I think it is safe to say I need a far deeper understanding of how Lc ties engines to stacks
As promised, here is the full layout of the experiment I was performing, which I'm sure someone else may have tried previously, but I never was able to locate any information about. That may just mean I'm a big enough idiot to embarrass myself publicly a lot
Back when I was trying to figure the Mc IDE out, I managed to score almost all of the remaining build platforms. I found that I could move them all over, and still use them to compile Mc programs regardless of the version of the IDE I was using. This is probably not news to almost anyone who was working with it back then, a boat I missed so I am playing catch up as it were.
My thoughts said that if I could do it in Mc, it *might* work in Lc, so my first trial was to move the arm engine to 6.5.2. Of course, the 6.5.2 builder program didn't see the addition in the linux panel, so I reversed course, and moved it to 8.0.1, which did see the engine folder and added the entry for it in the builder settings...

- Builder settings 8.0.1...
The first stack I posted here for testing I expected failure on because I hadn't changed anything during the save of the stack, i.e. it was saved in 8.x format, and was attached to a 7.x engine, which would never be able to run it.
For the 2nd test, I saved it from inside 8 as a legacy 7 stack, which I thought *might* work as the 7.x ide could now open it, and so the engine should be able to run it. Unfortunately, that didn't work either.
The last test you ran for me was using the 8.x ide to save the stack back to 5.5 format, which was going to be the best shot at having this work, and then saving it out to a standalone from within the 8.x IDE, but I guess I am just missing some key(s) for this puzzle.
My ultimate thought was that even though I don't develop for Pi, and generally avoid the later IDEs like the plague,
if it worked, people that like using the newer IDEs might be able to skate by till they have a working solution for those later IDEs (I think v10 was brought up).
I certainly want to thank all of you who participated in this without knowing the beginning or end goal again, it was for me a valuable contribution of your time, and it is really appreciated
