I like and use the MSD bigger gold colored race boxes with the proper coils, not any of the 6 series, on all of my race cars with compression and rev above 6000 RPM
Their is a world of difference on how much spark the race boxes will make and how high they will do that at or above 7000 RPM
I do buy and use used MSD7,7A,7C 7AL2 and 7AL3 with the proper coils, they will knock your socks off though so be careful around them
The first one I bought was a MSD 404B back in 1975, that box made my NHRA legal 426 Street Hemi motor start and idle a lot easier when cold and it would pull a lot harder in the summer in L.A. in the summer smog back then than the other two non MSD boxes I had used before then
IHTHs
I do have two new MSD boxes that I haven't used yet, a Grid and a Digital 7 non programmable