Back in the day when the MP-1 was designed it was meant to be an even-hotter-rodded Marshall typo sound.
They designed it around the Chinese 12AX7A (MP-1s were shipped with "National" 12AX7A .... MJMP pls correct me if I´m wrong).
So to get that most original MP-1 sound my way to go would be TAD 12AX7A-C as these are (imho) the finest Chinese 12AX7 tubes avlbl today.
The JJ ECC83S have a bit tamed high/higher end which (once again imho) makes them a bit more "pleasing" to the ear; their gain and sound comes from the mids.
Do some tube-rolling and find your favorites! NOS Balckburn Mullards sound awesome in the MP-1, as does the Re-Issues (which are, like the modern TungSols, made by Sovtek....).
If you play in band though you´ll come to the point where you discover that once the drummer enters the room it doesn´t matter what tubes or other snake oil parts you use