[Cobra 29]

I want to replace my Duraspark distributor with a MSD Distributor for easier tuning. Eventually, I will replace the current ignition box (a FMS part made by MSD) with a Digital 6 box. My question is should I select the MSD 8354 which will connect to the existing ignition system and later to the Digital 6 (I believe) OR get the MSD 8478 which requires a MSD box immediately? Are these two vacuum advance distributors the same except for the connection wire?

Additionally, I want to make sure I order the distributor with the right distributor gear materal. My 351 in the FMS M-6007-A351 engine. The specs say it contains a FMS M-6250-A351 high performance hydraulic camshaft (lift .520 intake, .538 exhaust). What distributor gear should I use ???