2.8 that doesn't oil the top end well

[Yank]

I have been trying to figure this engine out in my spare time. Spare time is getting scarce theses days so can you guys help me out? The top end isn't oiling the way it should on either side but the left side is nearly dry. Here is what's been done to it:

I had a head put on 6 years ago
It's sat up for three years
I replaced the lifter assemblies 2 years ago
oil pressure is 40lbs
compression is around 90 on all cylinders

I know it could be a clogged oil passage(s), a spun bearing, etc... Where would you guys start first. The oil rail is supposed to be full of oil or at least partially full...right? I've been thinking about pulling the oil pan for a look-see but I need cheaper less invasive ideas first. Thanks

 

[enginepaul]

If oil is going to one side and not the other, it is probably a blocked passage. You may want to take the rocker assembly(s) off and have a look. If the engine has a lot of sludge, be careful not to know anything into the oil passages.
The oil rail just needs to get some oil, not necessarily a flood; the rockers and valve tips should have oil getting to all of them.
You don't really need a lot of pressure and 40lb should do it.
Equal compression is a good sign but if the engine is high mileage and leaking oil, an overhaul may be in order.