Good for you! I tried pulling a water pump way back without pulling the radiator and it cost me. I nicked one of the radiator tubes and caused a pin hole leak. Tried to save some labor, but ended up costing me plenty to pull the rad anyway and now had to fix it. We live and learn!
Just place a piece of card board or thin sheet of plywood in there to protect the radiator. Oil pressure is fine as long as it doesn't cause a leak at the oil filter adaptor ring, add about 10 PSI for every 1k rpm above idle. Usually LA motors should see at least 50 to 60 psi around 3k and above. The P reg will not let it go much higher unless a H p pump is installed which is only set by the P reg spring in the pump. H Vol pumps have larger cases and gears but usually set P around stock and will show slightly higher P at rpm, then you can get H p H V pumps but as I said, watch out for leaks at the oil filter adaptor. Using a cast adaptor will make for insurance here, the stamped plate is a POS it will promise to blow out and empty your pan for sure if you raise the P. The whole reason for big pumps is for when the engine is built sometimes bearing clearances are opened up especially the side clearance of the rods which will lower Pressure and increase flow to cool the crank journals. A stock pump will not supply enough to maintain pressure here until the rpm come up and it will still be lower than it should be in most cases. For instance engines that have the pump in the front cover casting, a spacer must be used to install a HV pump, the only thing you can do without the spacer is raise the Pressure, open up oil passages so more can pass through which essentially does give a little increase in volume and decent increase in pressure. Old AMC, Buick, and 3.8l GM are some examples. All old MOPARs use either an external pump, slant 6 and BB or in LA, in the pan, like SBC's and Fords. Everyone went to direct drive on the crank snout to reduce parts. This has become a problem as the housings are made of cast Alum and they wear causing loss of pressure when the oil warms, the pump expands making the problem even worse. So much for improving quality.
Never considered any MOPAR with a LA or for that matter any engine they used back then to be limited on space around the WP. Now a slant 6 is a bit more cramped but still workable. The ONLY time I ever pulled a RAD was if the cam was coming out or the engine. But then I always had good tools and good hands. Put a piece of cardboard, plywood or sheet of thick plastic in there, I usually left the fans on the pumps and pulled the assembly and worked on it outside on dis assembly and installed pumps then added parts to re assemble to keep from messing gaskets up. JUST BE SURE TO GET THE RIGHT LONG BOLTS IN THE RIGHT HOLES !!!! I have seen a few engines that had ruined cylinder walls because the longer bolt was installed in the wrong place and tightened till it crushed in. It usually doesn't cause problems with the piston in that hole but it can crack a block letting coolant into the oil pan which is a BAD thing. I know most people know that when a bolt won't turn, stop trying to force it but here, these engines have bolt holes that go into the jackets and they rust making it hard to remove and replace bolts. Chase out the threads and use some sealant, NOT silicone but PTFE, teflon or permatex NON HARDENING thread sealers. NO teflon tape ! The bolts must be sealed to prevent leaks and corrosion inside the threads and inside the aluminum pump housing which can break bolts eventually when you have to replace it. A good practice is to coat the bolt shanks with aluminum anti seize also to help stop them from sticking inside the chain cover and pump.
10lbs per 1000 is the builders rule
