start with the basics
manual oil pressure gauge to see what your pressure actually is. some guys just leave them hooked up under the hood mounted to the firewall so they can do a check whenever they want but the gauge isn't hanging under the dash or somewhere less pleasing to the eye. these guys will usually also run an idiot light to signal them if a low pressure situation occurs. if doing that gauge under the hood thing use a braided line or a good pressure hose with some wiggle room for engine flex.
if the pressure is actually high then look for why. the relief valve is in the oil pump body and the stocker will usually be set at 50-70 psi I think. if you do the manual check and it is actually high and you are legit concerned maybe pull the pan and replace the pump and pick up tube. cheap enough for most sbc's but check your application because the first couple of years for the sbc had some differences. while there do a plastigage check on the bearings to see what you have.
how is the high mount filter plumbed in? those are usually a bypass filter so not meant as a full flow scenario I believe. they were plumbed into the oil gallery at the front of the engine and the outlet goes into the lifter gallery through the intake manifold. these systems were used on the 55-56 v8 engines and were only an accy from GM. otherwise there was no oil filter on the early 265, you just changed oil more often. they also have a different cam plug at the rear of the block I think. all the oil went through the engine system first and the last thing to see oil was the filter, which was the end of the line. there is an orifice in the housing to regulate the flow through the filter and also keep the oil pressure in the engine constant, it acts as sort of a backpressure regulator. not positive on that but pretty sure. the first couple of years for the sbc were not the best from an oiling stand point
a sbc pump with adjustable relief valve from jegs. good pic on where it is located for the regular sbc
https://www.jegs.com/i/JEGS/555/23501/10002/-1
a blurb from melling on pumps and stuff to check
https://www.melling.com/aftermarket-...u-k/technical/
a blurb from the hamb about a guy with your vintage engine that is looking for an oil filter housing cover gasket. read down some and see what the guys say about the early 265 oil system. maybe help you figure it out.
https://www.jalopyjournal.com/forum/...ilter.1040982/
another copy/paste with reference to the oil system on the early 265 and how it's oiling system differs from the later sbc a couple of years into production. just read down a couple entries
https://www.trifive.com/forums/archi...p/t-77754.html
good luck, keep us posted