I am far from an expert on kettle grills. The first kettle I ever bought was from a garage sale a few months ago. Folks on this great site provided info that I had purchase a Happy Cooker, not a weber, and it sounds very similar to the grill you found. With further investigating, I also learned the kettle I purchased also had the internal ash pan kneab explained earlier.
These are not the greatest pictures, and I did not clean completely before taking the pictures, but below are pictures of my lower bowl with the ashpan and a picture of the ashpan alone. If yours looks like mine, it might help start to point you in the direction of what grill you have? Just my thoughts and two cents as a very very novice in the kettle club.