Simon,
When you get the block back you'll see a few spots to get what you want, IIRC the factory spot is a pretty good location. IIRC it's located in the squirter galley? Second to last one pass side? Last in line would reflect the lowest pressure no?
Another option i looked into and haven't decided yet appears to be a good one. PARKER has hydraulic fluid remote filter mounts (400-500 PSI) as do all the big diesel repair shops, they are primarily remote mounted as well. Pick a housing that jives with your hose ID and put it wherever you want, some will have a high pressure spring in them to avoid popping the filter at 120 PSI. Most of these aftermarket remote monts have taps in them for pressure. Another company to look into is... crap forgot! Again! They have red filters...
Anyway, I got a 15 lb pressure switch and a BIG red shift lite if pressure falls below, could save me a bearing or two if I caught it in time.
Look around lotsa stuff out there. I find all kinds of neat stuff that's better at big rig shops and Parker, the saleman you get makes all the difference. At this point i have determined "Earls" is less than adequate.