[djnolan]

Judging from your picture of the coolant tank you don't have a oil cooler leak. What does the coolant cap look like underneath? White milkshake or clean?

You should repair the oil pressure gauge first. Easy fix, replace sender and go to auto parts store and buy some crimp on connectors.

You should be able to repair the OPRV without removing the oil cooler. Change the o-rings, degunk it. What else could make it stick?

If you have to remove the oil cooler, You don't have to remove the exhaust header to change the oil cooler gasket. It will slip out underneath the header. You just need to have a good set of wrenches, sockets, extensions, etc. to get to the bolts. And you need to get the gasket surfaces clean before reinstalling.

Removing the exhaust header is a *****. The flange bolts will be rusted to heck unless they have been changed to stainless. you will have to remove the studs or tilt the engine to get it to clear the frame to remove it. In this case this can all be avoided.

Just work on one thing at a time. Do easy things first. Don't panic...