Could I tap into one of the plugs on the back of my 350 block instead? I read somewhere that that gives a more accurate reading but I don't personally have any experience. I know on the front port my '76 350 got 25psi hot at idle and 60 cold with the stock timing cover, new stock gears, and the TA std. volume oil pump rebuild kit with wear plate. Even with the rod knock it held good pressure. Any input is appreciated.
Yes, http://www.buickperformanceclub.com/Oilmods.htm I have mentioned this before, but you will not see your lowest oil pressure until you measure it after at least 10-15 minutes of highway driving. That is when the oil gets the hottest. Depending on your bearing clearances, there is a drop off of oil pressure from the front to rear of the block.
Would this be a necessary mod for a 300hp and below build? Or just extra insurance? I have no real qualms about doing it, but it'd sure be a pain if it started to leak for whatever reason. Have to take the trans off/motor out to service it. I set all my bearing clearances at .0025 when I built it, and intend to do the same with my SP motor. Hell, I have the '76 motor sitting in my garage and with the rods out (in a box) I can wing the crank and it'll spin like butter for 2-3 revolutions with messed up bearings and all.
It isn't necessary at all. It just gives you an indication of the oil pressure at the rear of the engine. It shouldn't leak if done right. My 470 has a balance line done the same way as the 2nd method on that page I linked for you. 5 years plus, no leaks.
The only way to access oil pressure at the rear of the block is the right (passenger) side lifter galley pipe plug. This is easiest when the engine is out. To do it with the engine in you have to separate the engine/trans. remove the flexplate/flywheel, remove pipe plug, drill hole in bellhousing flange of the block to run your line.