Looking for info on vintage Celestion 12" 25M speakers.

[armstrom]

I'm going to be doing some work on an amp for a friend but I wanted to get some info up-front. The amp is an old Marshall SuperLead combo (Solid state) http://www.schematicheaven.com/marsh...__30w_2199.pdf

The speakers are 12" celestion greenbacks with no markings aside from the date code (at least that's what I'm told, I haven't had a chance to look at them personally). The schematic seems to show two 4 Ohm speakers in parallel however 2 Ohms seems to be pretty low for an old SS amp like this.

That leads me to my core question:
If the impedance isn't marked on the speaker is there an easy way to determine what it is? I know I can measure the DC resistance but is there a range the resistance will fall in to based on the impedance? For example, if I get ~6 Ohms for the DC resistance is that pretty much guaranteed to be an 8 Ohm speaker or is it possible for it to be a 4 Ohm?

The amp is dated from the late 60s while the speakers are from the early 70's, according to the date codes.

Also, does anyone know the power rating of these speakers? I would guess 25W because of the model number, but I don't want to just assume
-Matt

[tubeswell]

If you measure ~6R with your meter, its pretty much 8 Ohm impedance.

~12-13R is 16 Ohm impedance