When you adjust timing you slightly loosen the distributer bolts...enough to be able to barely turn it. With a timing light hooked up to the battery terminals, the pickup clamped around the #1 plug wire, and the light pointed at the pulley on the front of the crank, you'll see the timing mark lit up each time #1 fires. This mark will show next to a fixed measure (like a mini-ruler) on the front of the engine (I can't remember how it looks on the Montero, but you'll probably see a "0" with several tick-marks and a "10"). Tapping the distributer by slight bits rotationally in one direction or the other will bring timing forward or backward. Get it set to 7 +/- 2.....check idle.....get it set to 800 +/- 100.....check timing again (adjust as necessary).....check idle again.....you get the idea.

IIRC, the EGR valve is right below the carb. It's easy to get to. It's held on by two bolts and two hoses. When you take it off you might get away with reusing the gasket, but I'd suggest getting a new gasket (couple of bucks). Clean out the carbon any way you can but be careful not to damage the bellows. Carb cleaner helps nicely but try to avoid getting it on the bellows.