The lines are all plumbed AN, and are -12 in, and -10 back as per the instructions. As stated, the car had a sae 30wt in it and had no issue w/ pressure before. It HAS to be that oil that is currently in it that is to blame for the pressure loss. With regard to going to a 20/50...There has to be some degree of loss related to pumping that heavy oil through the engine regardless. There is no windage tray in this engine, and at some point I'd imagine that a counterweight sloshing through 50wt would have some degree of windage, in addition to whatever minimal loss comes as a result of having to turn that belt to do that.Here are my thoughts on the oil "thing". Oil works best when at a temp over 200* and less than 280* roughly. At that temp there is no advantage to running a "thinner" oil, outside of a few HP gain. A gain that I doubt you can feel. After all, how thick do you think 20-50 is at over 200*? At that point the "heavier" "thicker" oil has more stability to it. I run a 20-50 semi-synthetic in the race engine. This stuff: http://www.drivenracingoil.com/dro/xp5-sae-20w-50-semi-synthetic-racing-oil-16054html/ .Why this stuff? Because my engine builder highly recommends it and he has not steered me wrong in 20 plus years. I also have an engine oil heater that is attached to the bottom of the oil pan. Like this: https://www.wolverineheater.com/Wolverine-Model-16-250-Watt-Heater-p/16.htm. The engine does not get started until the oil is up to temp, which I guess works great for a race car that has a more scheduled run time, but could be an issue if you were going to fire up the Monster at a moments notice. You do live in a warmer climate so maybe not that bad at all. My guess is that your oil pressure would stabilize with a quality 20-50 oil in it. I don't remember what bearing clearances you had the engine set up for. I would also hope that the plumbing for the external pump did not have any hard 90* fittings as those kill flow. Everything should be done with AN fittings that promote flow without the pressure loss of a hard 90* fitting. Anyway, I know engine oils can be a controversial and/or emotional thing (just talk to an Amsoil person), but it never hurts to hear what has worked for others.
But compared to looking down at the oil pressure guage and seeing 5p.s.i,...I'll drain, and change that junk out in a heart beat.