No... You need to wait until he starts stocking Leopold FC700 keycaps. Pretty sure that the modifier keycaps would also not be the correct size (width), and your keyboard will end up having keycaps of different heights.
You can use the KBC blank keycaps
Weren't the ones I posted KBC keycaps? I am confuzzled.
The FC660M stock keycaps are similar in profile to the FC700R. As usual, Leopold likes to be special in their keyboard endeavors. If you look at the picture regarding keycap height, the stock FC660M keycap is slightly taller than Cherry profile but shorter than OEM. There is nothing wrong with the KBC Blank keycaps. The main difference is the height. They are OEM profile. If you have a chance to visit a Best Buy, Microcenter or Frys and check out the mechanical keyboards they have on hand like a Razer Blackwidow, Coolermaster Quick Fire Rapid, and the list goes on, they have OEM profile. Once you get your board, you'll notice that 660M has a shorter profile.
I mention having to purchase 2 sets because your usual ANSI layout will have only one 2.25x Shift key (the left Shift). The 660M uses two of them because of how they integrate the arrow cluster into the layout. You can buy one set of KBC Blanks, but you are left with having to use the stock 660M right Shift key, so the heights of your keycaps will be mismatched (mainly that one Shift key).
If you want a set that's identical to the 660M stock keycaps (legends and height), then by all means wait for a FC700R keycap set. You won't have to worry about the Leopold spacebar issue and everything else will fit in place. By getting the KBC blank keycap set, you'll have to be a bit creative by modifying the spacebar a bit and possibly getting a second set just to get a matching right Shift key (it's a pricier option since the only reason you want a second set is for one key
) The main point I was trying to make with my picture of the 660M with imsto thick PBTs was to show that the modifier rows and spacebar length can be swapped out with keycap sets widely available as opposed to early versions of the Noppo Choc mini and other boards that use different sized modifiers and spacebars. You just have to worry about that pesky right Shift key.
As Ivan mentions, Cherry keycaps offer a plethora of options. They have various keycap lengths (and of course the lovely Cherry profile) that will fill the FC660M and you can get creative there as well. I hope that clarifies things a bit and doesn't overwhelm you
