It's pretty straight forward, as this is what I did with my JDM distributor in order to run an external coil with the MSD SCI+ ignition. First off, I bought an MSD Pro Cap (dizzy cap) which obviously has the extra HT lead socket for the external coil. The MSD part number I
think is PN 8292. Just check it here -
http://www.msdignition.com/sci_8.htm
To wire the external coil into the dizzy, take a look at the instructions on page 10 here -
http://www.msdignition.com/pdf/6350_frm%2024381.pdf
If you want pictures of the wiring inside the dizzy, let me know and I'll PM them to your or whatever.