There are lots of tube possibilities and choice is very subjective. Basically you need a pair of low noise 12AX7 tubes. My personal preference for the MP2 are the New Sensor Mullard reissues, I've had some for a while now and love them. MJMP likes Ruby tested JJs. Here's a link to Dougs Tubes with plenty to pick from. The TUNG-SOL reissues would also be good (I've heard good things about them). (http://www.dougstubes.com/preamp-tubes/12ax7-ecc83-7025.html).
I mount my MP2 at the top of the rack as this gives some space above the unit. I rack the effects under it as they don't get too hot (or leave a space under it if you can).
The original tubes were Chinese 12AX7s, typically no brand on them, just some red writing saying 12AX7. And they will be way past their best if the unit has been well used.