Replaced washers in 50 plus yr old shower faucet but now I can't shut off the hot water with the handle

Try this.
Remove the stems again, check the washers.
Reinstall with the stems in the open position.

Assuming you mean you can't turn the water off completely, not that there is still a drip.

Have you checked the hot water seat for rust spots or knick? That would stop the water. Back to you, Tom