Marshall / Celestion Speaker Question

Guys (and Margaret),
I'm inquiring for a friend who isn't connected right.

He's got a late '70's Marshall 4x12 (we think, I haven't seen it). It's got the checkerboard cloth, corners, the *small* round plastic input jack cup, round emblem on the back (he says).

The speakers have a black label with gold lettering, and they say Made for
Marshall by Rola Celestion. There is a code on all four speakers which reads T3129. There is another code on all four speakers. Three of the speakers say GM16, and the fourth speaker says 3M12.

He wants to know what model Celstions these are. I don't have a clue.
Anyone?

That didn't come out right. I meant to say, he isn't connected RIGHT NOW (as in online).
That really *wasn't* another way of saying "he's a bit off" ~kp

Steve, I'll run these questions by him when I speak to him next. May be a few days though.