Do you have access to any kind of machining? If so, it's pretty easy to take the first two stages of gears out of the Kit of Parts FP gearbox and put them into a different housing that's easy to adapt to. Here's a photo of how we did this two years ago, but it does not have to be this complicated. All you need are two plates (1/8" or 3/16" aluminum is fine), some bearings, some spacers/standoffs, and two shafts. I haven't opened up this year's FP gearbox, but in the past the first two stages were either 32DP or 24DP gears.
If you have calipers, a center punch, and a lot of patience/steady hand, you could probably even make said gearbox plates on a drill press. It likely won't work as well as if machined, but it should still be feasible to make it work.