Just be careful. eBay tube vendors are hit and miss. He could very well send you the tubes with specs that will have the tubes bias within range for a mesa, but if he is inexperienced with the amps or was just telling you what you needed to hear to be sold that would not be uncommon.
So definitely when you throw them on there, look and make sure the plates don't turn red or that they are not giving a cold, harsh tone.
Years ago I got a Weber bias probe that goes between the tube socket and multimeter, something to check the current your tubes are drawing would be advisable. Then you could know straight away, the new tubes should draw around the same mA as the old ones