[Lynn Eades]

So Mariano, tell me what you intend to do with regards to an oil filter in your truck?
I assume you intend to run a bypass filter?
If this is your plan, then just tap into anyone of those 3 holes. All you are doing there is receiving oil under pressure.
I doubt that there is a plug (or restrictor) inside the horizontal gallery (where you picture shows the grub screw) If so, TAKE IT OUT.
You bypass filter will have (or should have) a restrictor in it somewhere(see Jacques post)
You need to return the oil from the filter back into the sump (Robs post) or through an oil filler tube with an oil return fitting in it.(Ford made them)

There is absolutely nothing wrong with a bypass filter. They normally have a finer media and remove more nasties. About once every 10 or 15 laps of the oil, it all gets to go through the filter, so over time it is all nicely cleaned.

The war time engines were swapped around a bit between trucks and carriers. This was o.k because there was nothing (no restrictor or plug) in there, in a Canadian or British carrier (the clever fittings did the job of restricting the flow, and sending it via the cooler). The complications came along with the Australian pattern carrier set up (same plumbing, different fittings, which required the restrictor plug) and the hot rod boys fitting full flow filters.
I hope that helps.