What is the minimum pressure for oil at idle speeds. Meaning when I shift into gear and ate only running around 700 rpm. It's a 1988 454/425.

In my opinion, 20psi hot in gear minimum. Below that, I'd say theres issues.

The previous owner installed auto marine pro comp gauges and didn't change the sending units so my gauges read backwards, I had a mechanic verify that. My port motor Guage shows 0 to 80 on oil and the mechanic says that 80 is 0. Last weekend I notice when the boat was hot, meaning running at specs, the oil pressure Guage showed 70 which would actually be 10, that was cruising thru a no wake zone. If I bumped the throttle to 1000rpms it jumped up to I would think is 30-40.

Obviously I need a new Guage or a correct sending unit to be accurate but what would cause the oil pressure to drop like that.

fix your gauge or put a mechnical one on first. Make sure you actually have a problem.

just because it reads backwards, doesn't mean it is accurate backwards. in fact you can bet it is off. you can tell you have more than 0, but that is all. get the senders that go with the guages, and put a mech on there to check accuracy.

I tried swapping the senders I can reach them without moving some major parts. I think I'd rather get new gauges, any suggestions. Bought a mechanical yesterday, I'm going to wire it where the low pressure alarm is temp.

Put the mechanical gauge in yesterday and fired it up. It reads higher then the auto meter if the auto meter reads correctly backwards. It fired up with 60psi cold. Didn't run it much just in the drive way. Can't wait to compare them when the motors warm.

60 cold means 35 to 50 warm. you are golden!! now fix the guages.