I'd try and see what happened to the MSD units just for curiosity. The ones i had were plagued with rust issues internally. And when the motors started to run bad i knew one of the advance springs had broken messing up the timing....after i sent them to MSD for a "refurbish" i sprayed them down with CRC to keep the rust off and they worked ok from then on out...but it was a yearly thing to spray them down at the star of the season to make sure i didnt have problems....

Never been a fan of the all in one units of any brand, never saw one that worked. I'm running a basic MSD distributor that's locked and using a Daytona Sensors box to manage timing. The Daytona Sensors will do idle control by using timing and it allows me to retard timing with a switched input when I need to run marina gas which is usually 90 octane vs 93. Still getting it programmed will have to report back when I get it set up.

Rust in MSD! I had a one motor last Saturday that was back popping, I was scratching my head wondering what it could be. So I pulled the Cap off the distributor and it looked fine. Then I looked at the Reluctor and it and the Magnetic Pickup, both had tons of rust on them!! I cleaned the reluctor up with emery cloth and the back popping / miss went away. Yesterday I reached out to MSD and asked of they have one that wont rust. They said the one treated with Zinc is for a Marine environment. So I ordered two and two more Pickup's. The Tech-line guy said Rust shouldn't affect anything unless the rust is coming off... By the picture, mine had a lot of rust!

The tech line guy said blah,blah,blah,blah,blah,blah,blah,blah.

The marine stuff has been rusting and running poorly for dozens of years.

Many Schit Daily

Mine were rusty too. Better pull the rotor and check the weights and springs. On mine, one spring was rusted in half and the others were in pretty bad shape. The weights were all stuck at full advance. Starter didn't like it much. Cleaned it all up and ordered more springs. Gave everything a light coat of oil and it's been good for 3 seasons.I connected the timing light a couple of weeks ago and verified mech adv still working. Need to open it up and re-inspect. See link for pics on post #23.
Loading up at idle

Prepare to be double pissed. Better buy a third box to keep as a spare.

MSD makes a box that you can program the ign curve but it's not cheap (or for marine). BTW, MSD boxes seem to live longer if not mounted to eng. Mine are mounted to glass using orig shock mounts and they're at least 7 years old now.
https://www.holley.com/products/igni...rip/parts/6530

You mentioned new builds. Lots of opportunities for variation in intake height. If it's a bit higher than expected, the teeth on the dist gear won't properly engage the teeth on the cam gear. If it just barely engages, it could run for a little while then die when gear teeth wear a bit. That's why I asked you prev if you confirmed dist was turning or not. You can usually tell if engagement is good by how much the rotor turns as the dist is seated the last 1" or so. It should turn abt 1/8 of a revolution as it meshes with the cam gear.

The types of metals for the dist gear and cam gear need to be compatible too. If not, the dist gear will wear very quickly. If turning a high-perf oil pump, it only exacerbates the problem.

you want even more problems? try this.........MSD sucks.