YEEEEEEEEEEAAAAAAAAHHHHHHHHHHHHH 2 CHANNEL DUAL BABY!!!! Nice choice man, looks like a fucking mint one, and I did a shootout between 6L6's and EL34's in mine a little while ago and found almost no difference, though I ever so slightly preferred the 6L6's. It's a pretty crunchy amp (bordering on harsh, but that's all in the tweaking) to begin with, so it really doesn't need any more coming from the power amp IMO. Here's the
shootout (though it was the first time I mic'ed it up, and I had the bass knob WAY too high, so don't judge me
) Plus, in the manual Mesa says 6L6's are more durable, so all in all that seems the best bet! As for models, I'd go for Ruby's if you're on a budget (they're still awesome), or Mesas if you're not (it doesn't look like it
)