Hey Richie,
Adjusting the valves would not effect the ignition timing. The valves should be fine, too.
If you think through the symptoms systematically you will rule out or in what it could possibly be.
The facts as I am seeing them:
- Happens on accell not decell, is dependent on what gear you are in, and was sudden in onset:
On accell your timing does change by increasing the degrees BTDC and if it were off it could cause predetination by not increasing enough. The thing is is that this problem was sudden. For your timing to have gone out instantly it would need to have something fail.
Since you now have a vacuum leak you may wish to check the connections on your vacuum advance can to see if this is not the fault. I would suspect if this were the case that you would also be experiencing backfiring pretty bad.
For the tranny, accell is when it is needing to push the 2000+ lb car thus it is when all of your internals are being stressed the most. On decell your tranny is only pushing the internals and the clutch disk so it is not nearly as stressed. Also, you stated that he noise is gear dependent. This typically will rule out your engine. If you rev your engine to a high RPM and hear the noise with the tranny in neutral you have effectively isolated the problem to the engine for most problems. If the noise does not happen, and thus only happens when the tranny is hooked up to the engine pushing the car then you ahve isolated it to the tranny. Do these checks and get back to us so we can isolate it further.
Be warned, there may be more than one problem
So isolation may be a bit difficult at times, but this should be enough info to get you into trouble.