[Hotfingrs]

Easy answer first, yes just extend the venturi tube. Drill and tap the end for a brake line fitting, then about another foot onto the end of the original clamp. The reason for the crazy readings was the reversion effect at the end of the exhuast, that's why you have to be in farther.

I think you're confusing the primaries and the secondaries. The primaries are the front 2 barrels and should have a PV. The secondaries are the back 2, and should not have a PV. A PV will enrich the circuit by approx 6-8 jet sizes, that why the jets are larger in the back then the front.

With your cruise figures you should be on the idle circuit at cruise, or just barely into the primaries at 2800. Do you have 4 corner idle adjustment, and can you hook up a vacuum line?? If you doand can. start with each idle screw out the same amount, then adjust each screw until you get the highest vacuum reading. They should all be pretty close to the same amount in or out. After you have the highest reading on all four, add 1/8th to a 1/4 turn more, you'll find it's to lean if you leave it there. Also drive down the street at your cruise speed and see what you have for a vacuum reading and how close you are to the 6.5 inches.

There doesn't seem to be a problem with your advance curve, Should start coming in around 1000 rpms and be all in by 2800-3000 rpm