Idle Rpm High in Park, Low in Drive

Your going to have to mess with mechanical in the distributor. IMHO, you have an issue that you have no idea what cam is in the engine. 10* initial timing is good or marginal for a stock 318, not for something that has a larger cam in it.

I would try setting the initial timing to 18-20* see how it responds at idle and in gear (RPM drop). Turn some initial timing in and get the idle down if possible. Don't drive it until you get the mechanical/total number under control. Engine timing is a four step deal; initial, total, curve and vacuum (if using). Total timing an engine is a horrible method for a street driven car.

If you are trying to use ported vacuum, put your vacuum gauge on the port at idle. It shouldn't have any significant vacuum reading, should be 0. If it has a reading the same reading as your idle, that's a problem. The front venturis are likely open too far allowing vaccum to hit the port.

I wouldn't mess with the vacuum advance as it's a fly in the ointment.