I have a home made grill, that has a propane connection. If I disconnect the propane and just use charcoal will that be OK? There are some stones or blocks in there. They did not come with the grill.

Disconnect and completely remove the gas line for a start. Can't say how well this home made structure will stand up to a char fire which can be much hotter than NG or propane. If those blocks are whireish fire bricks you should be OK

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Here are some pictures, does it look like it might handle it?

When I run out of propane I use an old large metal cake pan or broiler pan from my oven. I start the coals in a charcoal starter chimney and pour them in the pan and place on the grate above the burners on one side to bar-b-que.
Kingsford 5 lb. Charcoal Chimney

Doubtful this will last. Appears to becommon brick and plain mortar, both will crack from the heat of a charcoal fire

Try it. You can always insert another propane grill in there. They will be going on sale soon getting ready for winter items. Check Home Depot and Lowe's for sales on grills. Take measurements of your old grill so it will fit.