A good trick for removing gasket material from the decks with the engine still in the car: get a powerful shop vac and locate the nozzle right next to a fresh razor blade as you scrape old gasket material off. Change blades often, and be careful not to scratch the surface of the deck. Once you start to use a blade, don't turn it over, you will scratch the gasket surface. The vacuum will remove the material as it is scraped off, preventing it from falling into the cylinder, head bolt holes, and coolant passages. Rotate the crank so that each piston comes through top dead center, and vacuum the space between the piston and cylinder to remove anything that may have fallen in there. Make sure each cylinder bank has been drained of coolant before using the vacuum, otherwise, you will end up with coolant splashing into the cylinders from the vacuum. Put some oil onto each bore with your finger and rotate the crank again. any particles that are contaminating the bore tend to stick to the oil, which is left near the top of each cylinder after the piston begins its downward stroke.

Make sure to remove the cylinder head bolts in the reverse pattern of torquing, in a couple steps, just like when you torque the heads upon assembly. This will eliminate potential warping.

Don't use tri metal head gaskets unless you also are rebuilding the bottom end as well (block decks resurfaced). They only seal well on perfectly machined surfaces. For the typical head job, composite gaskets work the best. Use Mitsu factory gaskets or a higher priced aftermarket type (except for the Felpro blue, I've heard of poor results for those).

Make sure to replace all the stuff you can get to during this job (water pump, timing belt, cam seals and plugs, etc.).

Not a difficult job, just take your time and be meticulous.