Possible MSD 6AL failure

My 68 Cuda's using an MSD 6AL (6420, the analog one). A few weeks back, the car stalled out and would not crank over. It was a hot day but I hadn't been driving long. I had it towed to my mech and he confirmed that the spark was igniting so that wasn't an issue. By the time the car was at the garage, the car had somewhat cooled so other than a flooded carb, it did start. He warned me that sometimes the MSD can get hot so it may need to get cooled if the contacts start to separate, one of the reasons he stopped using MSD. He had the car for a day and didn't notice any other issues.

So last night I started the car fine. The car idled low and turned off, which I left to me not letting it warm up enough. I'll note that the carb's been tuned as recently as last week, so I don't think it's a carb issue. I tried to start it and it did the same thing as before and it wouldn't crank. After a few minutes to trying, it finally started and made my way gingerly home.

I'll add that the engine seems to run smooth, so I don't feel any misfiring.

This problem seems to be 6AL related as I've read similar issues like this. I've got a couple of questions.

1) Does it seem like a 6AL problem? If not, what else would I be looking at.
2) If it's a 6AL issue, I assume the only solution is replace the box?
3) Is the 6420 directly replaceable with the 6425? I'm hoping I can just swap boxes w/o having to mess too much w/ the wiring.
4) Since I'm already doing this, is there any danger to me using spade connectors on the wiring? My mech has a few boxes and it'd be good to have ones to swap out.
5) What's an alternate to the MSD solution?

Thanks in advance. This board has been a WEALTH of info, especially compared to other A body forums I've been on.