Welcome to Tractor Forum, woodie. I cant answer you question, but didnt want your first post to go by without you at least getting a welcome.
This wont help with your problem, but is something I found while researching in the hope to find an answer for you: Lilliston is no longer in business the rights to Lilliston brand mowers was purchased by Bush Hog and discontinued. This is a pity, as every comment I can find indicates Lilliston cutters were well built machines.
You write: It appears I need to back the tension bolts off and slide the gear box towards the rear
this may be a way to see the lube level, but is it also a way to adjust belts. Belts usually means finish mower?? Do you have a rotary bush cutter or a finish mower? In either case Im thinking it will be a load for the 8n you list in your profile. You will need a over run clutch if you are going to use your 8n to power it, especially if it is a brush cutter.
From what I read some of the Lilliston brush cutters came without slip clutches and stump jumpers, if this is the case with yours, you might want to be real careful, unless you install a slip clutch. 8n PTOs dont hold up well when heavy spinning blades on brush cutters attached to them come to a sudden stop.
Finally my usual safety comment: Be sure to disengage the PTO and wait until the blades on your mower has stopped turning before you leave the tractor seat.