I'm running a '68 350/350hp with HEI (with top coil) and have thought about adding and msd 6A unit, but it would would probably be a waste of money as the current setup runs damn good. On the other hand I do have a MSD 6A on my 57 Olds with the j2 setup as it is still using the original distributor with a Pertronix electronic pickup conversion and a MSD coil. There is no HEI available for the Olds.

In my opinion I would suggest you use the HEI and give your dad the MSD. But that's just my two pennies.