I know this has been hashed out a bunch of times but need some quick advice. I am pulling my motors to replace transom assemblies and want to address a couple of these issues while they are out. They are pretty much stock hp carb 502's, gen 6 blocks with gen 4 era accessories swapped over when repowered. Have always had issues with oil temps when running hard, pushing up close to 300 at times. Thinking first thing to check is the bypass in the block, what am I looking for to determine if its correct? Then I may put in some different oil coolers, not sure what they are now but probably stock off the old 454 mags. Would like enough capacity for future upgrades, so considering thermostatic coolers to keep temps correct. Any thoughts? Then I was also considering putting some water pressure reliefs on the back side of the intakes, I don't have pressure gauges and it concerns me, plus the added benefit of flow through the back cylinders. I have ports on the back sides, would run them to a tee then the pressure relief and dump either back to the thermostat side or overboard. Any input here, will work?

It sounds like you know the solution...larger oil coolers with oil thermostats. The water dump isn't a big deal unless your water pressure exceeds maybe 25 lbs. I agree that permanent water pressure gauges are not mandatory but you can get a old gauge and rig a hose it find out where you are. Anywhere between 10-25 lbs will work.
The low cost option is to do nothing but run a high zinc synthetic motor oil ($10-12 qt) and change it every season. It can handle 300 degrees in a non-race application.
Ben