IF the leak is coming from the oil pan gasket, you can do it, and while you are at it you can upgrade the front and rear main seals from rope to silicon. If it is the timing cover seal you'll have to pull the pan to get to the two bolts in the front bearing cap at the bottom of the timing cover.
I'd power wash the engine at one of those coin operated car washes- get all the grease and dirt off the engine and underside. (plastic bags and rubber bands on the carb, distributor and draft tube). I sometimes even take my set of ramps to the carwash so its easier to spray from below. After that if there are still some grease marks try brake cleaner and a tooth brush or green pad if neccesary. Then check it every day as it starts leaking to figure out just where it is coming from.
If it is the oil pan, there are a couple of things to keep in mind when changing a pan gasket.
Count the bolts, take them off, keep track of them and clean them up before putting them back on. Clean the gasket surface on the block down to bare metal. I usually use a razor blade in the flat scraper set up used for cleaning windows and follow up with brake cleaner on a rag.
First- clean out the pan real good when you've got it off. There's a good change it'll contain a layer of sludge. In fact, you might run some engine flush (or marvell's mystery oil) for 5 minutes before draining the engine. The older oil didn't have detergents and so the particals of gunk settled in the pan. Newer oils keep the stuff in suspension so the filter will catch it.
Second- Once its off you might have to loosen the crank to get the front and rear main seals out. Make sure you've got the torque specs and a torque wrench for this and to tighten the pan bolts. And since you've got the pan off, why not paint it and maybe carefully straigten some dents and dings?
Third- Before you paint it or put it back on, make sure and straighten the mounting surface. By that I mean using a hammer and dolly/anvil or other flat surface (vise?), to flatten around each bolt hole. There is a tendency for the metal around the holes to bow towards the gasket from tighening. If you don't get this surface flat before reinstalling, you may not get a good seal.
Fourth- 'glue' your gasket to the pan- put a bead of silicon on the pan, put the gasket in place, let it dry for a while. You can even put or tape a few bolts in the holes to line up the gasket
OPTIONAL- some people put Silicon on both sides of the gasket- 'glue' it first and then when its ready to mount put tsilicone on the other side. A little goes a long way.
Fifth - Slide the top half of the front and rear main seals in place and torque the crank bearing caps back down.
Sixth- RTV 2-B (or whatever you used on the gasket) on the threads of the bolts/screws- This is a non-hardening sealer and helps.
Seventh. Let it sit at least overnight before you fill it with oil.
Eigth- Since you've got it off nows a good time to upgrade to a magnetic drain plug. These are handy 'cause when you check the oil if there's anything on them you know something is up with the engine. Don't forget to replace the plasic or copper drain plug washer and keep track of the extras, you'll need them next time you change the oil.
Finally, DO NOT OVERTIGHTEN the plug or the bolts. Common mistake is to overtigthen these and squeeze out the silicon or crush the gasket or bend the pan.
