Best thing would be to hook up with someone that has a Champ or other single ended 6V6 amp.
Or just keep it safe as a spare for a rainy day.
For tube life, I think your amp would benefit from having 6V6 tubes that were a good match with each other. Reason being that both tubes, if evenly balanced, are working pretty much at max dissipation. If the tubes aren't evenly balanced then the hot one may be operating in excess of its max dissipation and so will wear out quickly.
Tube are a regular frequent consumable, with that amp especially, so you could soon build up a stock of odd ones that a tech may be able to match up.