Hey banbozny,
Both the PI and the PII require the 12 volt power source. The PI is not designed to use a 12 volt coil. So, you cannot eliminate the ballast resistor and hook the PI to the coil as a power source. The PII is the one designed to use a 12 volt coil. The ballast resisitor is eliminated and the unit is powered by the + side of the coil. This is a material improvement. So is the dwell control. I would not spend my money on the PI.
Regarding carb and dizzy. If you plan a carb update in the future you will, at that time, need to upgrade to the dual advance dizzy (68 - 73) as none of the popular performance carbs will support the dual vac unit on your car. The reason I note this is that the PII that goes into the dual vac unit will not fit the dual advance unit. So, if a change is planed you should do it at the same time.
Another point. The dual advance dizzy can be set up to run vary well without the vac advance at all. The vacuum system is not necessary to the performance of car. As a matter of fact, timing management is far more predictable without it. So, if you go this route you can install the dual advance dizzy (also referred to as the single vac unit) and the PII with you 1100. You will be very happy with this mod. PM me for detail if interested.
Enjoy - Steve