Hi, dark;
Well, the 'stock' gasket IS the steel gasket. All of the aftermarket gaskets are composite type and are thicker than the steel ones, which causes lowered compression unless the head is milled by the respective amount. For instance, the stock steel gaskets are about .020" thick installed, while the popular FelPro version is .055" thick installed. In an otherwise stock engine, using the FelPro gasket lowers the 1980 3.3L compression from the original 8.5:1 to 7.6:1 - dismal at best (I did this 2 years ago, not knowing it at the time, and being in too big of a rush to check). Ford made a replacement gasket of the composite type which is .027" thick as a fix for leaking head gaskets in warranty situations. I have a couple of these left for sale, if you want one. They seal better than the steel ones, which can be tricky to seal and assemble unless you're good at it.
In any case, if you pull the head, plan on milling it .010" - .020" and get a valve job. Then smooth the now-sharpened edges of the combustion chambers and smooth the ridge that will then be shrouding the valves. Reduce the boss around the sparkplug hole and remove the "bumps" that Ford usually left in the chamber castings. Get new lifters, too, GOOD ones, like from NAPA or Ford. All of this together will increase the valve lift and compression, giving better engine efficiency.
The exhaust port divider partitions the siamesed exhaust ports on cylinders 3&4, right under the carb. This was done to heat up the carb intake tract for better driveability and MPG, but today's fuels have such light elements (like ethanol) that it causes carb boiling and vapor lock. The exhaust port divider equalizes the flow from the 2 center cylinders for better engine balance and less exhaust manifold turbulence, which adds up to better breathing. It also slightly reduces the carb (over)heating problems. If you go for headers, you must get one of these, anyway, since this is the only way to seal the header plate - at least, on all the 3.3L headers I've seen...
