A 35 horsepower or greater engine size is what you would need for this with a standard single stage gear pump or a single cartridge vane pump which is even better than a gear pump.
A four inch ram will be much better for you to work with if you still wish to do this.
If you want a fun boring project fill your brothers OWB half full with firebrick and watch how much money and wood it saves him as you are increasing the thermal mass available to reatin heat and release heat back into the combustion chamber-I DID THIS and I wish I had done it 30 years ago!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
About your frankensplitter;
FUN projects cost money; A fun project would be combine the use of a small bandsaw mill and a chomper BUT not interfere with intake chute of the chomper by simply slicing the oversize logs and then having a live deck to feed the slabs to the chute to be winched into the chompers drag chute.
If you want twenty eight gallons per minute you have to have a tank that will carry and store more than 28 gallons per minute(most of 40 gallons of oil for a buffer) because of the surge of oil returning on the return stroke and that is a lot of money because you need a baffled tank with a top mounted flooded suction filter for the pump.
IF you want a pump look at a 12 gallon per minute vane pump for what you want to do with a 4 inch cylinder rather than what you are intent on buying.
Do not waste your money especially since its your money and try to reinvent the wheel.
IF you want simple, bid on or buy one of the small used chompers that is for sale and buy a small band mill to slice the oversize logs to a 14 by 14 size beam to feed the chomper.
do you happen to work for chomper??
and he's not re-inventing the wheel with this. the chomper isnt the only processor out there!
i would say look for a 3 cylinder diesel something around 40-50 hp
put a 2 section pump pump on it one for the splitting ram, and one for everything else
we made one
had a JD diesel out of a ingersoll rand compressor that the compressor was junk in.
had a 4 spool valve that ran the log chute, log clamp, cutting bar (up/down) and adjustable 6 way wedge.
the splitting ram ran off a solinoid valve controlled with a foot switch
and the cutting bar was ran off a hydraulic motor, controlled with a solinoid valve which was controlled with a proximity switch that when the bar moved down to make a cut it would turn on, and when the bar went all the way back up it would shut off.
really no need for a live deck unless your doing production, ours had just 3 6x6 beams which the logs went on then we would roll them into the chute.
we later replaced that with a live deck because we had one, this processor is a perminate unit in a 3 sided building (one side open to load logs onto the deck), has a sawdust blower which gets blown into a sawdust bin, splits come out of the 6 way through a chute then through a bar grate chute, then drop onto the conveyor, and into the dumptruck
your processor is in no way re-inventing the wheel, even if it was, how do you think the processors that are currently on the maket or ANYTHING for that matter came about??
