So I suspect need to replace at least 2 displays and possibly the master on my project Firepower... it's more cost effective to buy a replacement kit.

So if I buy a 7-digit kit (such as X-pin), will it be compatible with the rest of my original boards as-is?

I understand there are modified game roms available to make Firepower fully score with 7-digits. Others have done this while also changing to different MPU (Williams Sys7, or one of the aftermarket replacements). But can I use a 7-digit kit with a regular Sys6A MPU?

It's an interesting "what if", but after sleeping on it more I decided to stick with the 6-digit displays as a nod to the evolution of SS games since I have a 7-digit game in Space Shuttle. Besides, Firepower kicks my ass in the virtual version, so maxxing out a 6-digit score would be a nice "problem" to have