I upgraded my original distributor to MSD electronic and I think the timing is too far advanced. Causing rough running and overheating issues. Where is the vac advance bell supposed to be pointing to set the timing? The timing mark is showing up at about the 8 o'clock position. I also think the vac advance is supposed to be unplugged when setting it...Can anyone verify?

If I need to provide more info, please ask.

Yes, unplug your vacuum line and plug it while setting your timing. This might confuse you but it really doesnt matter where the vac can on the dissy is pointing as long and your #1 plug wire coincide with the rotor and then subsequent wires are in place from there and you get enough movement out of it to properly set the timing. So if your number one cylinder is at TDC you can pull your dizzy out and place it in any position you want as long as where ever the dizzy rotor is sitting that the number one plug wire is put in the cap right above that and then place the remain plug wire in the correct spot. So keep it simple, there is no reason to move anything unless you are setting the timing or the vac can is hitting something and you cant get enough timing set on it.. I am not sure I understand you saying the timing mark is showing up at the 8 oclock position, you mean 8* (degrees) timing mark? If it is 8*, then you are probably a little low on the timing and that will cause overheat and running rough. Turn your timing up to around 12* (12-14) While your vac hose is disconnected and pluged, then readjust your idle speed to what you want it to be and then make sure you plug your vacuum hose into Manifold vacuum. With the vac can hose plugged into Manifold vacuum, it will idlle slightly higher, just readjust it by turning it down to the desired idle speed. This will also help with the overheating issue. The manifold vacuum is the lowest port on the front of your carb (usually attached to the base of the carb) or a plug coming directly off the manifold. Plugging your vac hose into a ported port (a higher port on the carb) makes the engine run a little warmer, and these cars most of the time run better on Manifold Vac. This is also a area that drums up a lot of conversations and disagreements, but I can tell you that my 400 ran a lot smoother and ran a lot cooler and never overheated again, even in the middle of the summer in muggy NC.

I agree with most of Ordy/s post and as mention distributor timing can be subjective.

In regard to vac can position I typically set it mid-point between the firewall and the manifold facing left, [drivers side]. And yes #1 can be anywhere as long as the rotor is indexed correctly. I like to have #1 pointed toward cylinder 1 which is close to factory.

In terms of vacuum to the can, full vac will provide a faster vacuum rate which may not be desirable as it may not be compatible with the distributor curve. The distributor curve is set by the tuning springs which control timing ramp. For example if you have a low rear end gear, [4.11:1] you can ramp timing much quicker. And vice-versa, if you have high gear, [2.78:1], you'd do better with a slower ramp so it doesn't ping. Distributor tuning if done right can provide max power without pinging or detonation. I prefer to run ported vacuum [based off of throttle position] which was originally meant for the distributor. If you run full vac, you may need to slightly retard the timing to offset the higher/quicker vacuum.

re: overheating; my engine like many others ran hot with the factory high compression heads. The issue was low octane fuel and not being able to tune the engine without pinging. Now that I have ported 6X heads, I have more tune-ability in the timing and never overheat.