Have some questions.

I only add;

I purchased some Thrush turbo mufflers for my Magnum. Out of summit racing for about $20 a pop. I drive the car daily and just made a round trip from Centereach L.I. (11720) to the Poconos (?) Strousburg P.A. (Exit 309 off of I-80) without any complaint. There quite on cruise and growl nice when the hammer is down.
A quite ride is the first order of biz with this particular car. It also has headers.

The MSD 6 or 6A is what is most likely what you'll use. I have hooked up the MSD box to the MSD ignition box many times. The instructions are easy and simple to follow. A slight timing adjustment may be needed for best performance. Gap plugs wider. I went to .055 without any problems.
The hardest part of the ignition upgrade is figureing out where you want to mount the box. I suggest on the drivers side inner fender between the battery and the brake booster.
A worthy and easy upgrade to do.