Here's an update on my situation...
With regard to the SD-70, I once again tried turning off the clickety clack. I had no success with the engine sitting still, but I did it with it in motion, and it worked! I have no idea why. I'm gonna test it a few more times and make sure it stays fixed.
I also worked on the Decapod. I finally did a feature reset, and that worked. When I did it, the smoke unit was just billowing out smoke, but now that the engine is running at a controllable speed again, the smoke won't work!!! I tried pushing the smoke button, putting the smoke on max, and still no success.
I do find all of this quite frustrating, and for the life of me, I still don't know why DCS has all of these nuances and complications. Not to get anyone mad, but my good old plain Jane TMCC doesn't give me a bit of trouble. Well, I like MTH engines, so I'll just keep coming to this forum for help.