Internal 3.75 I'm a bit worried that I got them to cut it too short, we will see how it works out.
No worries, it's BBQ and steel. Run with it, if you feel it needs more later you can weld more on! Once you can stick two pieces of metal together anything is possible and easy.
The 1/4" plate for the FB will be new because I can get it cheaper than scrap?!
Sounds ideal!
Tom