Go to home depot, buy a larger multi gallon tank, and a rubber washer to seal to the toilet, and a new float valve mechanism. set the foloat valve to the highest level prior to spill over, and vioa, you once again have a multi gallon flusher!
Best get a new wall valve as well, they go bad and leak when messed with.
Thank you. I’m hoping to remodel the bathroom, including getting a new toilet. I’m all thumbs with plumbing, but a local plumber I use may be willing to make the fix.