AT540 was a popular trans model in the 80's. Probably still made. The PTO's of that era were available from Chelsea and Muncie which were rebranded Chelsea's until the mid 80's or so.
I have installed a bunch of them but have never run into one that did not have a drive gear in it as Grigg suggests. They are expensive and required a lubrication line to force the lube into them as the PTO opening was very high up on the side above the fluid level. To operate one must place the transmission in gear to stop the drive parts, then engage the PTO and then return the transmission to neutral (N)to start he PTO.
When you say central hydraulics I must assume you mean a crank driven PTO/pump, the way a mixer or plow truck is powered.? Regular dumps have no other hydraulic requirements than the hoist so transmission powered pumps are ther norm.
