Hi Dave,
I took a couple of pictures from an old copy of " Radio Simplified " published in 1923. These drawings are very close to what you have. I traced out your wiring and it looks like the tuner is missing and maybe a .001 cap across the head phone terminals. Use 45 vdc for B+ and 6 vdc for filaments. If the grid resistor you have is shot just use a modern one like Jr Tech mentioned. I used to use 250 pf for the cap and 2.5 meg for the resistor. Your circuit is regenerative. Your little radio looks like fun.
A tuning capacitor would connect at the unlabeled green line and ground connection side of your radio. Verify that the filament lights before connecting the B+, just to play it safe. Headphones should be 2000 ohms or greater.
Ed