Let's see if the OP comes back to check for responses...

 

I got an email back from RSD. They said they have a new version of the dummy cap that has a low fuel light indicator. I'm not sure but maybe this would fix the problem of the counter not working with just the dummy cap. Leaving the guts of the original gauge inside the cavity is a good idea and I might have to try that when I get ready to do the mod.