Is not the first time somebody makes that and that's what Don at FBO ( 4secondsflat ) made on its first aluminium box, HR688 to replace the A688 unit maybe 8 years ago, and after that he made the new HRR688 which is the one actually being sold with a complete new system. When I knew that about his HR688 box I got deeply dissapointed. I miss the original A688 box thought.

Nice! Have any pics / details on the wiring ?

Check out this link, its where i learned the details to do it. Its 10 pages long and lots of good info! i will tell you this, if you do it, use the old 4 pin HEI module and nit the newer 7 pin because i tried the newer 7 pin first and it added 10 degrees of advance at right off idle.
https://www.forabodiesonly.com/mopar/threads/hei-in-mopar-ecu-casing.252705/

Same hear as I grew up in the 60's and everyone always sad Japanese made stuff was junk back then.
I know I had put MSD on my sons Dart and my 63 and both cars started and ran the same on either ign. I only went to MSD because I like the multi-spark at lower rpm to help keep plugs cleaner on my 63 and I got it for a great price and since its a street/strip car and I run the jetting for mph at the track but I do lean down my IFR and transfer slot feed for cleaner cruising. I have not raced my 63 with the digital MSD 6AL unit yet but it feels and runs the same to me and my sons Dart ran no faster when we took the MP off and put MSD on his car. Dont get me wrong as I like the MSD but if you have a good ign on your car and then go to MSD I would not think it will run much different. Course if you ign is not to good then it will run better. And I like the MSD for all it can do as the one I have has the little dails to turn to set you rpm limit. Ron