So, tomorrow when you get going, make certain you can (1) find your timing mark located on a bracket above your harmonic balancer mounted on the engine block; and (2) you can identify where the bolt and lock-down plate is located for your distributor. The lock-down plate is located on the driver's side of the distributor at the point where the distributor drops into the engine. I believe the bolt is a 9/16" bolt - you can check this on your own. You'll need to grab a flashlight to see it clearly and understand what you're looking for. The bolt holds the lock-down plate securely to the engine and to the distributor - it keeps the distributor from moving. You DO NOT need to remove this bolt. You ONLY need to loosen this bolt enough so that you can turn the distributor. Perform this operation without the engine running first so you gain an understanding of the firmness and the amount of force required to turn the distributor. You're going to turn the entire distributor either CW or CCW - depending on your current ignition timing setting. Again, DO NOT remove the bolt, just loosen it enough so it remains snug but you can still turn the entire distributor. And, perform this operation without the engine running first so you gain some experience with locating the bolt, locating the lock-down plate, and turning the distributor. It's best if you can do this. Take a permanent marker (this is primarily because it's your first time at this), mark a point on the distributor cap and mark a point on the engine or valve cover anywhere in alignment with the mark you made on the distributor cap. This will provide you a REFERENCE POINT to return to in case you turn the distributor so far one way or the other you lose your position. You're only going to need to turn your distributor probably 1/2" - give or take. Don't be surprised if you mistakenly lose your position. With those two reference points you can return the distributor to the location it was located before you loosened the bolt and began rotating. You could also use a pocket knife and scribe a couple lines which line up.

 

Your timing INDICATOR is for a V-8. The timing INDICATOR is located on the bracket above the harmonic balancer mounted to the engine. The timing MARK is located on the harmonic balancer - that big thing which rotates on the front of the engine.
Ensure you can clearly see both the timing INDICATOR and the timing MARK. The timing MARK is nothing more than a line on the harmonic balancer. Don't expect it be facing upwards, it could be located anywhere within 360* of where the engine stopped. You may be able to visualize clearly when you fire off the timing light, but why wait to find it then. Get down and look for it and make sure it is clean. If it is not clean, clean the MARK (line). What I'd do is this. Find the MARK (line), clean it good, dry it well (clean with a non greasy substance like acetone or carburetor cleaner), grab a bottle of white nail polish, and very evenly and lightly score a line of white nail polish on the MARK (line) - following the contour of the line. This line will be your reference point to set your ignition timing. The timing INDICATOR has increments of TOP DEAD CENTER (TDC) - the single line on the bracket, BTDC (Before Top Dead Center) & AFTER TDC. The increments on your INDICATOR run from 14* BTDC to 4* AFTER TDC.

 

I play a lot of golf. Therefore, you're getting this information because there's a good chance I'll be playing golf; but, there are tons of folks on here who can assist. None-the-less, considering this is your first go at it, review this YouTube video. It's the best I could find which clearly demonstrates in proper English language how to set your timing. It's for a Chevy small block - the process is identical. Just follow the steps. Note the distributor is different than yours, you don't need to worry that this distributor is an HEI (High Energy Ignition) distributor, yours is a mechanical contact points distributor - both are timed the same. Note his timing light is a dial-back timing light - this is no big deal. He is setting his timing light to zero (0) - which will be the default of your timing light because you don't have a dial-back timing light. Watch the steps to perform the operation and you'll be well on your way to establishing the correct ignition timing for your 350 cid sbo. And, remember it's always: (1) Dwell Angle>(2) Ignition Timing>(3) Carburetor (which you set with your vacuum gauge). DO NOT attempt to bypass this sequence and think you're achieving anything by messing w/ A/F mixture screws before you finish steps (1) & (2) because you are wasting your time. And, remember disconnect and plug the vacuum advance while setting ignition timing. Hook up vacuum hoses after ignition timing and then set your A/F mixtures.

 

Thanks for taking the time to post that great well thought out tutorial on tuning @Vintage Chief Easy to read and understand.

 

Thank you, Lamar.