Spinning this pump on the 6 splined pto shaft can only get me 750rpm at 2200engine rpms, this is not enough to get the pressure. My options are 540/750 for my pto.
are you sure? the pressure is not a question of enough rev.
the Pump develop 160 Bar in any RPM range provided that your Tractor have enough Power on the PTO to handle the 25ccm Pump. the only that may vary is the L/min or let me say the Gpm at different rev.
SO, what I'm going to do is to modify the pump shaft to fit over the tang on that upper pto shaft which seems to be spinning at engine RPMS, thus I can run the engine at 1500rpm + and get a decent pressure out of the pump, given that it has a nominal 2000rpm, I think 1500 engine rpms should be ok.
like i say before, the Pressure that the Pump develope will be the same, it does't matter if you run the Pump at 2000, 1500 or at 540/720 rpm
what you need is Flow and this will be with the 25ccm Pump at 2000rpm round about 50 L/min, at 1500 rpm 37,5 L/min, at 720 rpm 18 L/min and at 540 rpm 13,5 L/min.
it means, that the 325 Pump have nearly the same Flowrate directly driven by the PTO at 720rpm like the Standart Factory Setup with 310 Pump and 3,8:1 Gear Ratio Gearbox at the 540 rpm PTO.
it means also that you need to run the engine at the same (in your case 2200 rpm) speed to get the same or nearly the same output with booth Setups.
so In essence, the factory should have put a gearbox on that black brackt to step up the speed, or givien me somer kinf of adapter to hook up to the shaft above the 6 splined PTO. Or a pump that could generate such pressures with 540/750 PTO rpms.
If you try to run the Pump directly driven by the inner PTO (in your third Picture) that seems to spin at the same speed as the Engine don't forget that you need about 14,8 Kw or it will be 19,68 HP of your Engine Power to drive the Pump with the nominal specification and at 1500 rpm about 11,11 KW or 14,9 HP.
Don't know if your Tractor can handle this without Gear reduction.
i will not smash down your ideas, these are only the things that come to my mind and advices i will give you.