I did manage to try it out on Sunday afternoon. It wasn't a total failure, but it wasn't a great success, either.
I plugged the filter assembly as a closed loop into the main PTO circuit, oil hot, engine idling. I turned on the PTO and the filter inlet pressure went to 25psi. I slightly increased the engine speed and the pressure went over 30psi, which is the limit of the gauge.
I then removed the quick-disconnect from the filter return hose and stuck the end of the hose into the tank fill port to make an open loop. This gave me 15psi at idle. Again, the pressure rose very quickly with increased engine speed.
I suspect that much of the pressure comes from restrictions in the plumbing. Replacing the 1/2" outlet hose with a 3/4" hose might help further, if it's actually needed. If I go that route, I will make up an adapter to go in place of the filler cap in order to secure the hose and keep crud from falling into the tank.
The filter is rated for a maximum pressure of 125 psi, with a bypass valve that should open when the pressure drop across the filter is 25psi. From what I can tell, filter element replacement is recommended at a pressure drop of 15psi or so.
The filter housing only has drilled and tapped gauge ports on the inlet side, so I have no idea what the actual pressure drop across the element is at present. It does have a boss for a gauge on the outlet side. I think my next step will be to drill & tap that boss and add a second gauge. Then I should be able to monitor both overall pressure and pressure drop.
I'm hoping that I will find that my original closed-loop configuration will turn out to work acceptably, since it's more compact, simpler and easier to connect without introducing contamninants to the system. I doubt that it will be practical to use it inline with working implements at full throttle due to the potential for pressure spikes. I suspect that setup would require either a larger return line and tank fitting, or a considerably higher pressure (and cost) filter.
I'll try to get the second gauge installed by the end of this weekend and report the results.
Gravy