Can't say 100% from the pictures, but it sure seems that you have the upgraded MQ transformers and chokes. Since the transformers (top side) haven't been coated, you will probably find some nomenclature on them that will say for sure. One thing is certain from the picture: the output transformers are not the stock ones.
So, to get back to your original question, you may indeed want to modify your amp to use the 6EA7. IIRC, this will require replacing one cap and one resistor on each channel in order to change the bias to an appropriate level for the different tube. So, not a terribly elaborate modification; but, you will need the construction manual.
The manual is in the form of an Adobe file on a CD-ROM. If you didn't get it when you bought the amp, perhaps the seller still has it. If not, you will want to contact Bottlehead for the info.
If you decide you like the different tube, then, of course, you are done. If you want to change back to the original 6DN7, you will have to change the resistors back to the original value to return the bias to the appropriate level; the caps won't need to be changed back.
Nice looking amp!