You'd need more than one set to pull off a full swap -- the
left right shift of the fc660c is shorter than that of the 87U, and the bottom row has _six_ 1.25x keys, whereas the menu/winkeys on the 87U are 1x.
I was interested in trying this, but I'm really not interested in paying EK over $200 for keycaps (they've already gotten plenty of my money
).
I may at some point try just swapping out the alphas (the profiles match fine, so that's not at all an issue), but there are no in-stock colors at EK that have me excited enough to buy them right now.
(EDIT: fixed some typos)
EDIT2: Upon further thought and analysis, it looks like you'd be able to do this with an 87U keycap set plus an additional modifier set -- the left and right shifts seem to be the same size. That is much more tempting...