I've used the J&S on my F6B without the adapter; no issues from what I could see.

The J&S has two rubberized strips on top of the two support arms and the adapter simply looks like it stacks up a few extra layers to bridge around the oil sump. When I had my bike up on the lift I didn't detect any high-load points or instability without the adapter but if it really bothered you a couple strips of hard rubber garage door gasket material could easily suffice.

Note that the J&S uses the center stand as a lift point, so you need to lift from the side-stand. But, be forewarned, if you have a lowering link on the bike you may need to roll the bike onto some 1x6 boards to get addition clearance unless you have a helper who can stand the bike up.