OTC is good brand for quality--or used to be. The adjustable idea is great and if I had to do more cylinders I would go that route.
Somebody at one time tried to get the tops off these with a punch and kinda messed up the holes so I used an 18" pipe wrench to loosen them, then BIG channel locks to un-screw them. These tops are kinda soft steel so gotta use caution with them.
I think whoever tried to unscrew them didnt take the little lock screw out. -- they are very small and always on the underside of the cylinders. Th 580ck backhoe has the same design on its cylinders and that was where I learned about the lock screws.
Some cylinders have a snap ring on top and that style is a real pita to get apart.

"A machine you build yourself is a vote for a different way of life. There are things you have to earn with your hands."