After thinking about everything, I went ahead and actually went with the CircuPool instead, while I wait for that to arrive I got a check valve and jandy valve and quickly realized that adding the heater bypass may be a lot more complicated than I thought, if possible at all. Should have measured better first, heh.
With the check valve installed straight out, I don't think I have enough room with that and an elbow and going up to get the ring for my filter off. My only option then is put an elbow up first, then the check valve, then a tee, two elbows then back down in front of the jandy valve and back out to the pool. Like this, if you'll excuse my quick and dirty diagram from the side view (green is check valve, orange is jandy, grey salt cell, purple flow switch, blue existing valve back to pool/spa) - not to scale, of course. It feels like that will be a
very tight squeeze to get all that in that way. I'd probably have to put the valve handle facing away towards the check valve to get it all to fit.
It looks like I might just barely have 12" -14" between the heater and the salt cell with the flow just past the cell - depending on how big they are, i'll measure when it comes in tomorrow. If that's the case, should I just abandon the idea of the heater bypass and going up and over?