the jubilee was built with an optional live pto meaning some had it and some did not
if the tractor has a live pto it will accomplish this with a two stage clutch
the clutch pushed all the way down will stop everything pto and forward movement
a two stage clutch will disengage the forward motion when pushed to a point all most all the way down, but will leave the pto running until clutch is fully engaged
there are three types of pto system in American tractors,
1. standard manual pto is driven by the transmission and only runs when the tractor is actually moving, this was prevalent into the early 60's on most tractors as base standard equipment,
the fact that your grinding gears after the pto is engaged leads me to think that it is a manual tractor, and the pto can not be spinning when you are attempting to put it in gear
2. the live pto is still ran from the transmission but now has a separate clutch for the pto operation this is either done with a two stage foot clutch as in the old fords/Ferguson's, or with a hand clutch such as on the old two cylinder john deeres and allis Chalmers tractors
3. the independent pto ( independent of the transmission)is what is sold on most modern tractors, where the pto can be engaged and disengaged with just the lever or electric button (like on a lawn mower) without touching the clutch at all. however many of the smaller new foreign tractors sold today do not have this as a part of there tractors
the override clutch is a must for the old non live pto tractors, (especially for someone who is new to this type of equipment) a implement such as your bush hog will continue to spin (kinetic energy)and therefore continue to push the tractor forward,and there have been many incidents where tractors have been pushed into fences and ditches and novice operators hurt and killed through the years
get you tractor and bush hog together on a good open piece of real-estate, and put the transmission and pto in 1st gear before you let out on the clutch, then let the clutch out slowly.. if the bush hog starts spinning before you start forward motion on the tractor then your tractor is equipped with a two stage clutch and live pto, if the pto and forward motion start at the same time then it is a non live pto.
the override clutch is not that expensive and I would get one A.S.A.P. even if it is a live pto tractor that is just a good safety device
check out this video at 6.40 it tells about pto operation
PS
looking at your screen name I am thinking you might be in KY, I am in hart county and if you are close I will gladly let you come buy and try out the different types of pto operation since I have something with all 3 types and let you pick my mind on things that might interest you about tractors