Good question John, I'll try to answer some of these things.
Joe, I see where you asked about a VR throttle body but that's not what you need if you have a car with vacuum switch gear. This system uses a constant vacuum throttle body to make it work properly. It would work with a VR throttle body but not as well as it's supposed to.
Vacuum Advance:
system has no vacuum applied while engine is at idle and vacuum will increase as RPM climbs. System needs about 6 - 8 inches of vacuum to move vacuum cell to full position. Distributor may loose some timing advance at WOT. All vacuum advance is gone at idle or when coasting down hill when foot is off accelerator.
Vacuum retard:
constant vacuum signal at dle. As RPM's increase, vacuum signal decreases. A spring inside of the vacuum cell provides the advance movement. Since vacuum is usually high at idle, this system provides a constant zero positio for ingnition timing. Timing is not affected by WOT yet still returns to zero while coasting with no throttle pressure. Not affected by low manifold vacuum as much as vacuum adance systems.
Constant vacuum system:
throttle body maintains a constant vacuum signal that is switched off via a vacuum switch over valve at about 2,200 RPM. System is similar to VR but the vacuum movement is programed to happen all at once. The CV distributor is designed to have a smaller mechanmical movement and a larger vacuum movement than a 051 VR unit. The 061 and 062 units will move the timiing below the normal 8 degrees BTDC at idle to 4 degrees ATDC at idle. This is supposed to reduce NOX somewhat. The VR and CV systems will both give you about 38 degrees of total advance - they just do it in different ways.
The CV distributors will mechanicly advance up to about 2,200 RPM, then a speed sensor will trigger the switch over valve to close and the total lack of vacuum will caus the distributor to advance all at one time up to its full amount.
This system also employs two thermo switches that over ride the switch gear. A switch in the engine block remains closed until it reaches about 65C and then it will open so that vacuum is restored and the timing will move to retard. This feature helps the cold engine warm up faster. A second switch in the thermostat housing closes at 100C which causes the distributor to advance ( no vacuum signal) which will increase idle speed with the idea of cooling a hot engine. My thoughts on this idea is that it's probably too late to do much good on a hot day once the engine is at, or over, 100C. A 95C switch would probably be more usefull to get the temperature down before it gets too hot. I`m not sure if this switch is availble but I think it would be a better choice.
A VR throttle body could work on a 061 or 062 distributor but the advance curve would be altered significantly.
