i need an overall opinion on a msd 6a

The multi spark box's are an excellent item to not gain, but rather recover what the lesser ignitions lose out on. Under 3,000 RPM where they multi spark, it is a great helper in;

making the most of your fuel.
better starting
better running
more mileage

If you get a good box go with it. Just leave your stock ignition intacked just incase it fails. That way you just unhook the distributor and plug it back into the OE set up and go.

For surley open up those plug gaps! I went to .055. I may have been able to go further with a gain to be seen.
You'll also probably reset your idle down some.