There are two thoughts on this, one leave it alone, the other, clean it out.
For a truck not used much, leave it alone, change oil when its dirty, and go about your business.
If you plan on driving a lot, clean it out. Pull the pan, valve cover, and side cover and scrape out what you can. Then using a cleaner like mineral spirits or carb cleaner, flush out the remaining bits. Clean the covers and install new gaskets. Change oil when it gets dirty.
I have power washed engines just like this when the covers were off. I used a spray degreaser inside and out, very hot water, and 3500 psi, the crud comes off very easy. The water dries quickly when the block is hot, plus I dump plenty of oil over the moving parts.
Once clean, oil choice doesn't matter, what ever you like. A leave it as is engine, stick with a straight 30w oil. Modern detergent oils carry the crude with it so the filter can clean it, straight oils tend to let the crude settle out faster, thats why old oil pans always have a thick layer of deposits in them.
Its said, detergent oil can start to clean up and carry deposits from old oil, and with out a filter, the dirt can damage bearings.
Joe