Before you add a bypass filter, with it's limitations, you might want to ask yourself "why wasn't there a filter already on the truck?"
I noted on my 56-235 clean engine of unknown mileage, that removing the bypass filter and plugging the 2 ports improved both my idle and cruising oil pressure by 5-7 psi. Recognizing that the bypass filter dumps filtered oil back into a pan full of unfiltered oil, seemed counter-productive when I was more concerned about lubricating my bearings.
If your current engine has decent oil pressure it my have no adverse effect. However, if the PO had removed it to salvage an extra few pounds of oil pressure you might be going the wrong way.
Modern oils, changed at regular intervals (2-3K miles) seems to me, to be more prudent. If you pull the valve cover and your engine isn't full of sludge, I'd feel safe running a good quality straight 30 weight detergent oil that met API certification requirements for medium duty gas engines. If it were sludged up, I would hesitate to run detergent oil without some kind of filtration. Non-detergent would keep her running until it was time for a rebuild. Hope this helps.
Dave
