I was fortunate to save my factory ford manual when I sold my shop and so I have the actual Ford spec’s on the D6TE-HA distributor, which the manual says is the distributor for the 460 engine. It states the mechanical advance is zero to 1900rpm. 14 degrees at 2800rpm and 21 degrees at 5000rpm. The vacuum advance is zero degrees at 6 inches Hg and 28 degrees at 16 inches Hg. The static timing is 12 degrees do the math and it is a total of 60 degrees while cruising. This seems a little high and is why you get surging while cruising.

I had to replace the vacuum can with a replacement several years ago and it surged so bad that I had to pull the vacuum line off of it. I tried adjusting it with the allen wrench and discovered that it would only adjust the amount of vacuum needed to start pulling it in and would not control the total amount of advance. I put the light on it and the darn thing would max out at 32 degrees, which is way too much. I put a 4/40 screw in the activating arm to stop it at 18 degrees max. (Pic attached) The vacuum actually turned out to be 21 degrees total.

I ground out the 10L slot on the distributor upper advance shaft to get a total of 21 degrees max. With the static at 12 this gives me a total of 33 degrees advance at WOT and 54 degrees max at cruise. This way I can finally get the thing through California smog.

Does anybody have any opinions or advice as to what I did right or wrong. Any help would be appreciated.

 

You don't add the vac advance to the mechanical advance. The vac advance is only there to give some mpg gains at lower rpms. Initial + mech should be around 35 degrees, all in at about 2500rpms.

 

A 10L slot is 20* of advance already.
Why would you need to file a few thousandths to gain one more degree?

Yeah, the stock vacuum adjustment changes the spring pressure.
There are other advance cans that will adjust the limit.
But by increasing spring pressure the vacuum advance falls off faster as the throttle is opened.