There are ready made FCR39 kits for the Suzuki DR650, it's one of the best mods for that bike (and probably others), you might have luck checking out some of the suppliers and thumper forums for ideas on what works and what accessories are available, there may be adapters meant for other bikes, that might work for you.
Iirc I think I recently saw a pair mounted on a racing Kawi EX500?
The FCR39 was stock on a few KTM motocross bikes, and Yamaha motocross and 4 wheelers, & others ?; the FCR39 on my DR was a home built kit by a previous owner, I "think" using the carb from a Yamaha YZ450 or Banshee.
I can't remember the fine details, but there are slight differences in the different carbs for different model bikes.
With the advancements being made in 3D printing and materials, is that something that might possibly work for you?
If you could get it to work, your gas mileage would suck, and it might turn into a fussy starter, but I think you'd notice a huge performance difference depending on what carbs you're running now.
Good luck
