I made one about 3 yrs back using the tractor (MT180D) hydraulics aux output.
Essentially it consists of a 5' long 6" I-beam with a pair of ears to accept the cylinder pin.
The ears were 3" X 1/2" flat stock mounted vertically at the 3 pt end. This was about 16" higher than the upper face of the I-beam and served as the upper 3 pt mount.
For the lower mount I simply welded a suitable length of shafting with a backup washer and drilles for linch pins.
I welded the splitter fixed at the tail end and devised a sliding pusher plate (about 6" X 6") from heavy (5 5/8" plate) welded to an appropriate slider base with ears to guide along the upper I-beam face.
To the rear of the push plate I welded a suitable short piece of pipe to act as a socket for the cylinder push rod.
A simple hole drilled to match my cyl rod acts as a 'pull back' for the push plate.
The ears have a bottem retainer (1/2 X 2") to prevent the pusher from jumping off.
The slider was made longer than wide to prevent it from binding sideways. All slider measurements are very 'sloppy' to prevent binding.
My MT180D pump is 2.5 GPM and the cylinder is 4".
While I might like it to be a bit faster it sure is not lacking in power.
Fast enough to tire me out after 1 hr or so, so I guess it's fast enough.
Hydraulics is straight fwd plumbing with quick disconnects for ease in setting up.
Lever arms with springs can turn the splitter into self return and position stopping.
With my FEL it balances out fairly well, but then I do not drive fast with the splitter mounted as that's a lot of weight overhanging the rear.
A very nice feature is that you can raise the splitter to suit your 'aching back'. Also it is easy to reposition when the wood pile gets a bit cluttered.
Just for fun I occasionally 'cross cut' 6" maple logs just to show off.
Certainly beats swinging an axe!
All in all I am very pleased with the results (and my welds)
My total costs were I-beam ,about $50.00 and the cylinder (scrapped bulldozer lift cyl) about $20.00 some plumbing and a scrounged valve for about $60.00.
Balance was from my 'precious pile of (someday) scrap pile'