[Excaliber]

I'm not getting a good feeling about your mechanic. The knock is really simple and it's two things:

1. The timing is to advanced, plain and simple.
2. "Modern" gas, UNLEADED will be fine, use Hi Test if you don't want to change the timing. The T-Bird's were not high compression engines, thats why I suspect it's a simple timing issue. NOT carb.

Now the tricky part is: You can't trust the harmonic balance to be accurate on a car that old. SO correct timing may not be that easy. I would simply back off the timing a little at a time until the knock is gone AND the performance is acceptable.

So why is unleaded gas OK with an old car like this? Lead is a lubricant to the valves, specifficaly the valve seats. At SUSTAINED freeway speeds for a LONG period of time using unleaded fuel on an older motor could cause valve related damage.

Sunday driver, little old lady, NON sustained speeds unleaded fuel will NOT be a problem.

Now go fill up with some good unleaded Hi Test and get back to us.

As mentioned above dwell meter can be deceiving and give you bad results. Match book thickness is indeed close enough. Coke down the carb works, but so does plain water. That was actually a GM warranty procedure for their big 454 "putt put" owner engines.