I still don't have a great resource for dating the different MSD boxes. I wish there was a Day 2 specific forum or resource place.
I can tell you form first hand experience, that early MSD7a box you've got there does a great job handleing a Tunnle Ram on the srteet.
I did have an issue with it melting a hole the size of a quarter in my HEI rotor a few times. I did solve it with a copper coated carbon button.
Anyways, way cool man! Thanks for sharing the old picture.