The answer is no. The spacebar fits, yes, with an MX slider, but it will not be stabalized and is therefore unusable. The stabalizer spacing on the 86U is at 6u. Yes you read that correctly. You can mount and stabalize a 6u MX center-stemmed spacebar from GMK, but SP does not make a 6u spacebar for SA or DSA. To mount an MX 6u spacebar requires you to harvest the stabalizer sliders from a Novatouch. It would also look silly putting a 6u spacebar on a 7u keyboard.
The only way to support a 7U MX spacebar is to move the spacebar stabalizer holes on the plate to the right and left. You need a custom plate or you need to hack your own plate with a CNC or laser cutter. You also need to manufacture a new 7u stabalizer wire, as Realforce only includes 6u stab wires with their keyboards and the Novatouch, RGB, and Topre clone keyboards only include 6.25u stab wires. These wires are not compatible with costar or cherry stabs, except for maybe the clone boards like the Plum87, but then you would need to cut costar stab holes into the plate anyway for them to work.
PerniciousPony's solution was to modify the spacebar with clay to glue a Topre slot into the 7u spacebar with 6u offsets.