I scoured the forum for an answer but I came up with nothing on these specific questions.  Please let me know if I missed something.

I just bought an '85 SN2001 that has a recently rebuilt 351 engine (~30 hours).  I've been working my way through some minor repairs that the previous owner said haven't been quite right since the rebuild and I need some advice on an oil pressure issue.

The oil pressure gauge maxes out 80+ immediately after the engine turns over and stays there regardless of engine temp.  I double checked the visible wiring, replaced the portion of the oil pressure sender wire that was hidden inside the conduit for good measure, then moved on to the oil pressure sender.  I took it off, hooked up a manual gauge and sure enough it was the problem.  However, rather than reading the 40-ish psi I expected it started off at 70, creeping down to 60 after the oil warmed up to temp.  I ordered a new sender and while I'm waiting for it to arrive my questions are these:

Question #1: Since the engine is recently rebuilt, is this higher pressure to be expected?  I've read a lot about tolerances being much tighter on rebuilt engines which suggests that this could be related to the sudden change in how leaky the 351 probably was.

Question #2: I'm planning to change the oil before I winterize and my gut is telling me to change to 15w-40 oil like Valvoline Premium Blue to bring the pressure down and prevent any unnecessary problems down the road.  Are there any known issues, long or short term, using this oil in a 351?

Question #3: Am i missing something that I should be checking out before changing the oil type?

Thanks in advance,

-Bryan

I think you missed the part where you mention what weight oil is in it now 

If these readings are while it's on the trailer warming up on a hose, I'd get the boat on the water driving around so there's load on it and see what the oil pressure reads at different speeds/rpms after it's been loaded for a while

You might find that a new sender doesn't fix your issue and that you need a new gauge also, but after the new sender is in, you'll know if that's the case .

Also if you have a Pleasurecraft 351, most any High Volume pump won't fit inside the stock (rear sump) oil pan without some serious hammering and banging because it's taller than the normal pump and you can't bolt the pan down.

Thank you both for your replies 

You're spot on, it is a PCM 351.  The oil pan looks new and hasn't been hammered on so I have no clue if its big enough to accommodate a high volume pump.  I suppose I'll find out when I change the oil.

The new sender comes today so I'm going to get that installed and see if the gauge is okay.  I actually bought a new gauge already but then realized the more likely culprit was the sender and held off on replacing it.  Assuming I get the gauge issue worked out today I plan to take her out tomorrow morning to do as you suggested and let the engine fully warm up.  The 60-70 was using the fake a lake.  Then I'll decide on what weight I should be using.  Hopefully my timeline works out because I want to get this figured out before winter sets in. Overnight temps here are getting cold and I probably shouldn't hold off much longer on winterizing. 

It sounds like regardless of which weight oil I decide to go with, stick with 20w50 or change to 15w40, I won't be doing any harm to anything like the distributor or pump.  Is that a fairly safe assumption?

Way too much work 

You won't harm the distributor or pump or anything else with either oil, like MrMcD said .

Zinc concentration always sneaks into the conversation with flat tappet engines and your Premium Blue being a diesel oil has a decent amount of zinc, and with a little Google magic you can find out how much from the PQIA. 

They test oils for all kinds of stuff

Here's a link to your Valvoline Premium Blue15w40  test results showing plenty of zinc and phosphorus to keep most anybody happy.

http://pqiadata.org/Valvoline_Blue_15W40_4192017.html" rel="nofollow - link

You can surf around the PQIA website till your eyeballs and brain are tired of reading about oil, it's a good outfit