The MSD box and coil together should give you a plenty hot spark..

Double check the gap in the distributor, and wonder if the MSD was hooked up backwards if it would give similar issues? (the trigger wires to the distributor that is)

Once you get the ignition side of things checked for sure and can see you have a nice hot spark, then move on to checking carb maybe, etc...

(When I ran the 6AL and MSD coil on my Oz Charger, I could lay a plug wire on the valve cover with no plug in it, and you could see the spark jump from inside the wire to the valve cover.)