Distributor choices for a Magnum

A pertronix will NOT work with the sniper at all. And an hei unit will not allow you to control timing if you want that feature.

If you want the most budget option, that will allow you to do timing control also...here it is.
TSP-JM7613R Mopar SB Pro Series Pro-Billet Electronic Distributor. Red Cap

And this rotor.
Adjustable Race Rotor MSD Ignition 84211 - Pace Performance Parts

I do member discounts. Let me know. Hopefully you didnt buy the sniper elsewhere yet, because I could have saved you $ 100