NO NO NO, do not switch components around, keep them stock.

Man, I would hate to have that decision.

You say the Miyata fits you better? Then that's the one to keep, your comfort is more important then newer technology. Besides that older Suntour stuff was bulletproof, more so than than the newer crap they make today. I would keep the Miyata, if the Accushift thing turns out to be a hassle simply go on EBay and buy a long cage Suntour Cyclone Mark II GT, or Mountech II GTL derailleur and swap the two out but keep the Accushift. With the Mountech you do have to keep the derailleur clean and not let dirt get into the pulleys, but it will reward you with the fastest shifting derailleur in the world in it's era for mountain bikes or touring bikes.