Sounds reasonable given your mods...
I've never bothered to check mpg, but I do know this. With just headers/air filter, I used to be able to make it from here to Bowling Green on one full tank.
520 miles - 18.5gal tank would be 28mpg, so I was averaging better than that.
I've been there twice since heads/cam, and know I can no longer make it on one tank, but never calculated to see just how bad it is. May have to do that next May.