Sometimes old timers will disable glow plugs because they like to use ether and ether and glow plugs don't mix well. But I've never seen anyone actually remove glow plugs.
Often the threaded plug in the intake port is where an ether injector is placed, although a few Diesels will have an intake glow plug and one in each cylinder, my Duramax Diesel
in my truck is the only one like that I have experience with like that.
Glow plugs are usually wired in series which means when one burns out, the remaining ones get more current
and that can cause them to fail pretty quickly one after the other.
Every glow plug I have ever removed had soot on it, which makes me think they were in the combustion chamber, which means if removed, you would lose compression, yours have been removed without plugs being installed where the plugs go? Or did I mis-read that?
I have a lot of Diesel experience, but almost no Marine
Diesel experience, so take my post with a grain of salt