You can use the port closest to the firewall for oil pressure gauge or you can install a tee and use the factory pressure switch for a dash light and an external pressure gauge. That is the port gm used for the pressure switch and is a direct feed from the oil galley.
The port closest to the front is where the oil filter, if you use one, dumps the clean oil. It is a drilled port, not connected to an oil galley so you can plug this one up. If you look at the passenger side of your head, about the middle, you should see a square head plug. This is the same style plug gm used for the front port when the car or truck was not ordered with an oil filter.
The only other things I will mention, using a filter or not using a filter, your choice. If you are dressing up the motor with say a aluminum side plate, the 55-57, and maybe the 53-54 and 58 blocks, I forget right off the top of my head, use a steel line behind the side plate that connects a port from the rear cam bearing boss and runs to a port just under the square head plug I mentioned above. This is the oil feed to the rockers. If you look at the stock side plate you will see a bubble about the middle top of the plate. This bubble accommodates the fittings for the line where it connects to the inside of the block. Many times the aluminum side plates do not have an accommodation for the fittings so it will not fit with the fittings in place. So what you can do is remove the steel line from behind the plate and install plugs in both ports. Then you can run the out put of the oil filter, or tee off the driver side rear port, remove the square head plug from the outside passenger side of the head, and run a small 1/16 I’d line right to the port. If using a filter, you are now feeding the rockers with nice clean oil.
Finally, that steel line, and the rear cam bearing port canoften become clogged over time, especially with an older original motor. When this happens, the oil supply gets cut to the rockers which eventually ruins the rocker adjuster balls and galls up the rocker shafts pretty good. Really messes them up and they are hard to find in nos and expensive to rebuild. Rocker arms unlimited in California are the best when it comes to rebuilding old style shaft mounted rocker arms. Can also happen when the rear cam bearing becomes really worn, for what ever reason. The oil pressure bleeds off through the increased clearance of the worn bearing. The aftermarket used to sell these little kits to plumb oil from the driver side port to the port on the side of the head to feed the rockers as a quick and cheap way to solve the problem of a clogged line without having to take the side cover off and clean out the line. You can duplicate that with a couple of brass fittings and some small copper line (like the type used for an oil pressure gauge). Same rule applies though. Bigger is not better. Small Id lines only.
As for lines, when I needed them, I splurged a bit and used autometer stainless braided lines for a fuel gauge. I mounted the remote housing onto the inner fender well.
https://www.autometer.com/4an-braided-stainless-line-kit-3ft.htmlNot the most inexpensive of lines, but I had the same set installed for pretty close to thirty years and no failure of the lines. That worked for me.
