How to Properly Set Ignition Timing?

I believe ive read that article before. Then how come with full manifold vacuum hooked up, when cruising at 70 i was turning 3000 rpms( the car has a 700r4 overdrive trans and 2.73 gears)and with a ported source connected it cruises at 2000. The engine is also a 71 model year 350.  

Chevman,
That's because the full time vacuum port advances the timing more and even when it is not need at idle and I would recommend time ported vacuum port for the vacuum advance only. It can also cause detonation hooking the full vacuum to the advance canister.  
Horsepower sells Engines and torque wins races.

Then how come the person that wrote the article is dead set on full manifold vacuum for the vacuum advance canister? Vacuum is non-existant at wide open throttle though, right?
The vac advance was hooked to full vac for a while and i was constantly fouling  and damaging plugs. I spent more money than i care to mention on spark plugs because the vac advance was connected to full vacuum. Now with it on ported i havent had issues with fouled plugs and the engine is starting to run as it did in my truck. I forgot to mention that i have the heavyest springs in the mechanical advance so it wasnt an over advancement of that.  

I do not know why they are dead set on full vacuum advance.
Yes vacuum is non existent at wide open throttle.
Like I tell people I know there is good info on the net and bad info on the net so be careful who you get your info from..  
Horsepower sells Engines and torque wins races.

Just out of curiosity what heads are on your engine and what plugs are you running?  

Engine RPM at a given speed has absolutely nothing to do with ignition timing. The factors would be transmission ratio, rear axle ratio and tire diameter. Torque converter slip, if any may also have an affect. The only logical explanation for your claim, is that the trans was not shifting into overdrive for what ever reason. If your engine will foul plugs with the distributor connected to manifold vacuum and not, connected to ported vacuum, then you have some other problem you are covering up by doing this. The heavy springs will only raise the RPM that mechanical advance comes in. Doing so will help with a detonation problem, if you had one, but you may be leaving some performance on the table.  
Jim
70 El Camino
461 solid, m20,
pics in readers rides

The heads are stock(882s) with r44t acdelco's. Ive also used the NGK equivalent, as well as r45ts, accel shorty (8199) and the autolite equivalent all with the same plug fouling and damage. The r44t plugs have run the best without fouling/damage. All of the current r44t plugs are a golden brown color.
I just ran a test. I left all the timing the same as well as the jets. All i did was switch to a full manifold source from the ported. It started easier but under heavy acceleration it would not accelerate like normal, it was sputtering like the mechanical advance wasnt advancing fast enough or it didnt have enough fuel. the distrib has an adjustable vacuum canister so i can mess with that. My air/feul monitor also indicated a lean condition under heavy acceleration. At 70, my rpms were approximately 2750.  
So i pulled off the interstate, switched it back to the ported source and it drove normally. At 70 it was at 2000 rpms. Im not sure if when it was connected to the full vac source that it shifted into OD, but i know it did when it was ported. How could the vac on the distrib effect OD on the trans?  
I know its not fuel pressure related cause i have a brand new 250 lph electric fuel pump with adjustable pressure regulator, and pressure is at a constant 5.5.  

Timing does effect cruise RPM the higher the timing the higher the cruise RPM will be and that is a fact I have had so many people tell me it does not but bottom line it does.  
Horsepower sells Engines and torque wins races.

Interesting discussion, too bad it ended.  

I am staying with manifold vacuum, everything is running well now with no pinging.  The settings are ~30 degrees BTDC at 2500 rpm with vacuum disconnected.  I have the lightest springs in with a Mr. Gasket kit and 4 turns out on the MSD adjustable vacuum advance can.

This is my first experience with automatic transmissions.  The discussion above about the engine rpms changing with timing settings has to be a function of what is happening with the automatic transmission.  With manual transmissions the engine speed (rpm) is fixed based upon a specific car speed (mph).  The manual transmission gearing, rear end gearing, and tire diameter are all fixed, so it is impossable (unless you are coasting) for the engine rpm's to vary with car speed (mph).  

Now, I don't know how automatic transmissions do their thing, so I guess it would be possible to get different rpm's based upon how much you need to use your right foot to get to a given speed (mph).  And that may change with how well the engine produces power at a given timing setting.