Vacuum advance for 1970 was connected thru a solenoid and shut off until Top Gear using the transmission switch to allow or deny vacuum to the advance in the factory setup. The debate is split among car guys as to which carb hookup to use ported or manifold attachment on cars without egr and pollution controls. The consensus seems to be that you set your timing and idle with the line plugged off on carb and then try each hook up and see what works best for you. I have a 1973 400 in my GTO and all the pollution gear is removed. I recently fixed my advance and so far have found manifold or below the butterfly to work best for me but, as I stated some swear by the ported or above the butterfly hookup and a pretty good arguement can be made for either way depending on your application street or strip. Most strip diehards disconnect the vac and dial all the advance into the initial and mechanical combined so that at wide open throttle all the advance is present. I recently went to a car show and believe it or not the guys with aftermarket or hotrod parts had evenly split on the subject and neither could be persuaded.
Remove the distributor cap. Remove the hose to the vacuum advance. Remove the two screws holding the vacuum advance on. Install in reverse order.
800rpm manual transmission, o degrees advance 1200rpm automatic transmission 4 degrees advance
If it is on the front of the carb then it goes to the vacume advance on the distributer, if it is the big one on the back, either the shift down if you have auto trans, or uasualy pluged if you have a manual trans.
S&S Super E Carb Carburetor
Assuming you are running a point type distributor a Pontiac typically likes 12-14 degrees initial advance. This is also a good starting point for HEI.
with the engine operating temp and (if applicable) the vacuum advance undone and the vacuum line plugged up. it should be a 14 degrees before top dead center
On the carburetor
Which 454? The LS5 and LS6 are two VERY different engines even though they are both 454's. Timing specs are different as well. 8 degrees before TDC at idle will work for either, but may not be optimal.
One place to get parts for a 1970 Pontiac Grand Prix is at the website Stock Interiors.
Yes, the original chassis service manuals. You can find them on eBay from time to time. Not too hard to come buy.
If you have he intentions of overhauling it then the instructions will be with the kit.
There were 2,170 convertible GTOs in 1970.