Continued Oil PSI concerns

[D2Denny]

My G-75 has the END673 engine. Fresh 15W40 Delvac oil , clean screen in the pan, no visible signs of excessive wear when I pulled the pan, new 750 style filter in the can. Running when warmed up at highway speed have 25 PSI and idles at 5 PSI.  Truck has a WGB model WB-2 Oil Clarifer bypass filter. The truck build line sheet shows a 485GB filter assembly installed at the factory. Don't know if these are the same. Anyway, I have included a photo of the oil distribution plate on the left side of the engine. The small line coming off the T goes to the OIL PSI gauge and the larger line to the rear goes to the oil filter. (Is this the proper location for the Oil PSI gauge?). The bottom line partially hidden under the T is the return from the filter and dumps back into the pan.  I suspicioned that there was excessive flow through the filter and the oil pump could not keep up. I removed the filter feed line and blocked it off. Started and ran the truck up to temperature. Oil Psi at idle is now 15 and 40 at highway speed. My question is does anyone have info or literature on the WGB oil filter. Is there a restrictor fitting or metering orifice in this filter assy?? 

Also in the photo, the #4 line running up to the left goes to external oilers to the rockers. This could be another source of excessive oil flow demand reducing PSI. I'm going to pull the valve covers and see if the rockers are oiling without the external feed and possibly delete this feature. Any ideas on this??