MSD 6AL and MSD Pro Billet Distributor: Using stock tach on my 71 E body

[DocMel]

Im running a MSD 6A and MSD Pro Billet distributor (mag p/u) on my 71 Cuda, 440.

I want to run the stock dash tach:   I understand  need a MSD tach conversion adapter.  What part number do I need and how is it wired?

I have one gray wire from the MSD distributor that is for a tach, but of course, it doesnt work on my stock tach

[DocMel]

Anyone?        Bueller?.............Bueller?...........

Bottom line the MSD distributor sends out a signal the stock dash ralley tach will not recognize.  Tach converter supposedly fixes?

[HP_Cuda]

MSD tach adaptor #8920

OR

Look here:
http://www.msdignition.com/products/accessories/tach_adapters/

[DocMel]

The MSD lists a tach adapter for a MSD distributor, and another for the MSD ignition box.   

Since I am running both the MSD distributor and the MSD ignition box, which of the two adapters do I use?

[HP_Cuda]

Again looking at the list it looks like you need #8920 so you can get signal to your old tach.

[Chryco Psycho]

Send an EMail to MSD

[MizzouRT]

   I have MSD ignition and wanted to keep the factory tach.  Restoration shop that did the work is mostly a Chevy shop (they are Chevy guys and that is were the volume is in any case) so they called MSD tech support to get the right adaptor.  Some vendors are helpful and others not so much.  I recall them giving MSD tech support high marks and everything worked as described the first time.