I am not intimately familiar with your model, but it is similar to my B2410 in many respects - the location of the PTO drivehaft specifically. The slip length of ANY PTO shaft should be such that while operating, the OAL of the "slip" portion is evenly divided as follows:
1/3 "free" to driven (tractor) end
1/3 of overlap in the slip joint
1/3 "free" at implement end
]───≡≡≡≡≡≡═══[
⅓ male ⅓ overlap ⅓ female
The 1/3 does NOT INCLUDE the yolks, but is ONLY relevant to the amount of freedome of movement in the slip joint itself.
Take any PTO shaft, if you extend it fully to 40" and compress it fully to 22" you have 18" of free movement in-out. Of that 18", 1/3 (6") should be "free" on the PTO and impliment sides with 1/3 (6") of "overlap". Quick measurements with a tape will confirm this.
This configuration allows for articulation w/o binding of the slip joint and w/o dange of the slip joint being pulled apart during operation, all while allowing for eough overlap in the male-female slip joint to keep wear within acceptable limits.
So, you can trim the inner (male) and outer (female) shaft as much as you need to accomodate your particular installation. Just make SURE you have at least 1/3 of the total "slip distance" in "overlap" to reduce the risk of pop-out and excessive spline wear.