Any vac advance that has a hex shape in the housing can be adjusted. If you insert a 3/32 hex key into the fitting you can thread in-out a plate that is trapped in the hex. This primarily changes the amount of vacuum needed to start the vac advance moving. The amount of max advance is set by the particular part you have but by adjusting the cut-in you can also have some influence on the max amount because you run out of range or do not produce enough vacuum to pull it all the way. Like anything, the first thing you have to establish is what vacuum you have at idle and at light throttle cruise. The best plan is to make carb adjustments to maximize vacuum. Then record what the reading is as you drive the car around. There was an article on another website that gave the step by step on this whole process. In a nutshell, you want probably around 15 deg max on the vac advance and that will come in at idle and at the cruise throttle. By getting the additional advance in these situations, you will burn the fuel in the engine instead of in the exhaust manifolds, producing more power and less heat into the coolant. Just for interest - the max advance in distributor deg is usually stamped in the arm of the vac advance unit - double this for actual crank advance. If yours is too much and creates pinging at cruise you can get another unit (pre-1970 years will have a better range) or you can crimp on a piece of metal to shorten the travel of the arm.
