That's as simple as turning the distributor clockwise/counterclockwise a few degrees. But first, you need to make sure that your distributor was dropped back in exactly in the same spot that it was before. I'd venture to guess that it's either a tooth or two off (which is not really a big deal, you can just dial that timing back in with a twist of the distributor) or it could possibly be 180 degrees out, in which case you'd have to pull the distributor, turn the rotor 180 degrees, then re-install.
First, make sure you've got the engine TDC (Top Dead Center) on the compression stroke of the engine. To do this, you need to bump the engine over using a remote starter switch (or a buddy at the key) with the No. 1 spark plug out of its hole, and your finger blocking the hole. Don't worry, the piston won't bite ya.
When I say bump, I mean bump, as in just tap the starter. Whenever the compression stroke is coming up, air from the cylinder will force your finger off/out of the hole. That's when you should stop bumping the starter. Take a look down at the balancer for your timing marks...look for a hash mark on the balancer, it should be at or very near the 0 degree mark on your timing tab (if there is one there -- lets hope that there is). If it's slightly BEFORE top dead center, get a breaker bar (you won't be able to turn it with a regular ratchet unless you put a whole lot of hiney behind it) and a deep 5/8" socket and turn the engine by hand until the timing mark on the balancer is on 0 degrees on the timing tab. If the engine happened to land after TDC when you stopped bumping the starter, it's best to spin the engine TWICE more over (two revolutions of the engine to get back to compression stroke) instead of trying to turn it backwards with the socket.
Now that that's over, pop your distributor cap and see which way your rotor is pointing. It should be pointing down toward the No. 1 cylinder, or at least to the post that you have a wire running to the No. 1 cylinder. Most drop in their distributor with the wiring plugs pointing to the right, so that the post just below it (going clockwise) is the No. 1 cylinder.
Once checking that your rotor is pointing straight for this post on the cap, check your firing order. I'm sure you've already got that, but just for reference, it's 18436572.
Beyond that, once the engine fires up, you can
time an engine by ear, if you don't happen to have a timing light. If you've got a light, (standard inductive is what I prefer) hook it up to your No. 1 spark plug wire, and the battery clamps to the battery. Point the light at the balancer/timing mark, and pull the trigger. Advance your timing til it is ~8 degrees BTDC (before top dead center). This is something that you'll have to experiment with, because different engines with different components will run more efficiently on different timing settings, depending on intake, cam, carb, exhaust, compression ratio, etc. While you're setting the mechanical timing, set it with the engine sitting at idle speed, the vacuum advance unplugged, all vacuum ports on the carburetor blocked off. You'll probably have to go back and forth adjusting your idle speed and timing til it settles in right. You might find it runs best around 10 degrees advance, maybe even up to 12. I only recommend 8 as a conservative place to start. Should you hear it start to knock/ping, STOP advancing the timing, back it off about 3 degrees, and leave it there.
If you choose to attempt to time the engine by ear, it goes just as that last line in the previous paragraph -- SLOWLY advance the timing, drop idle speed to keep it at 850-900 rpms, wherever the engine wants to run. Keep doing this until the engine just begins to ping, then back it off a few degrees, and tighten down the distributor clamp. This method, however, is NOT recommended to most since it is only a very rough guideline to get an engine running. Using an inductive timing light and vacuum gauge is the best and only real way to truly time/tune an engine.
Once you get the mechanical timing set, you can plug your vacuum advance into a timed vacuum port on the carburetor, adjust your idle mixture screws, etc.
Let us know how it goes.