Hi Andy. It's hard to prove a negative, so all I could really say at this point is that I've seen no evidence to suggest any of your queries would have a positive outcome.
There are a good few variations on the Slow Motion theme, but these are all differences in the packaging rather than the content. The white labels and promo versions are off the same matrix press as the general release. I'm not aware of any different mixes of the album, but there are some variations in timing of the singles mixes, Day And Night being particularly variable. Diligent research by another Forum contributor has shown even these to be not quite as different as was previously thought.
The gatefold sleeve suggestion probably came about as a result of the UAG29765 reference, which indicates UA had originally planned it as a gatefold. This was quashed by all the shenanigans with the Rick Griffin cover painting. I don't believe any gatefolds were ever issued. The USA and Canada editions (both LA 345 G) also suggest an intended gatefold release there, but single sleeves were all that escaped.
There's no record (forgive the pun) of any MAN releases being issued on the RCA label. Not yet anyway.