Howdy Pills:
I'll give your Questions a shot.
"How can I visually tell the differences in the DSII dizzy?"
Other than the vacuum cannisters, there are very few, very subtle external visual differences in the DSII from somewhere in late 1975 until the demise of the 200 in 1983. There were differences on the inside due to specific applications. Mostly in the size, shape and weight of the centrifugal weights and stiffness of the springs. Another variable was the amount of vacuum advance allowed by the pivot of the advance plate. The vacuum cannisters varied internally in the amount and rate of advance. Many cannisters had an adjustability by inserting an Allen wrench into the end and turning- tighter for less, looser for more, within a built-in range.
"visual differences in single and dual advance?"
The dual vacuum advance cannister has two attachment niples, one is the usual location on the end of the cannister and the other between the distributor and the cannister. Both likes go to a pre-programmed vacuum switch that goes to several vacuum sources. This system was used with the later Carter YF, but mostly with the Holley #1940 carbs. Both offered ported vacuum sources. For a dual vacuum advance system to work properly, all hoses and switches need to be in place and functioning properly. Unfortunately, different applications used different configurations- similiar, but not the same.
"What problems will I run in to if I get a dual advance?"
The problem will be in hooking up so that the advance system works like you want and the retard side does not interfere with it. Many, including myself have used this system and just left the retard side alone and unplumbed. the next question will be, "does this cannisters built in vacuum advance profile fit my engines needs?" If it does, Great. If not, you're stuck with it. It is my experience that dual vacuum cannisters do not have the internal Allen wrench adjustability feature. If the vacuum advance is too much, you will be stuck with reducing initial advance or making internat mods.
Given a choice, I'd go with a single vacuum advance cannister, but the advantages of an electronic ignition system over a point system far out weighs the problems related to a dual vacuum cannister. Go for the ignition upgrade under any circumstances.
I hope this is helpful to you.
Adios, David
