There are a number of postings about using a Banebots (
http://www.banebots.com) 42 mm gearbox with the F-P motor. Banebots has stopped shipping the previous version and is supposedly going to introduce an improved model - but that has been delayed.
We used these last year for our lift and it worked very well. You have to remove the pinion from the F-P motor and press on the pinion that is compatible with the banebots gearbox. The pinion used to come on the motor that came with the gearbox (RS-550 type), but you can also purchase them separately. The F-P motor has the same mounting threaded holes and shaft size as the RS545-550 motor. I just checked the site and it looks like they are about ready to make what they call the P60 available which will do this job. Comes in 4:1, 16:1, 64:1 and 256:1
Good luck.