These are two pristine vintage Heppner alnico speakers I just harvested from a Hammond L-133 organ. Codes printed on the rims (575429/575439) indicate Heppner (575), the 29th and 39th week of 1964.
These are quite nice, clean for their age, no holes/tears in the cones, no moisture damage noted; no voice coil rub.
As you may know, Hammond often paired up tone-matched speakers in their organs with internal amplifiers; one was a smooth cone to carry the higher frequencies, and the other a ribbed cone for the lower frequencies. Likewise, these two could serve as an excellent 2 x 12" guitar cabinet. The two amps in this organ were each capable of about 15-18 watts of power (the main amp with 2 X 6V6; the reverb amp with 2 X EL84). I'd say that you could run anything up to 20-25 watts through such a 2 X 12" cabinet. I've heard anecdotally of people running a 50W amp through a pair of just such Heppners (but YMMV!)
I have wired up many cabs over the years with these types of alnico speakers from Hammond organs, from 10's, 12's and 15's (for you Stevie Ray fans) and played guitars through them with everything from Fender Champ clones to Princeton and Deluxe clones and 18W Marshall and Carmen Ghia clones, to great effect. Never had a problem with anything like overpowering the speakers, just nice cone breakup at higher volumes and warm distortion.
BTW, these speakers are each 16 ohms impedance, so wired in parallel, you've got a nice 8 ohm cabinet. This organ also had an original Gibbs reverb tank; that is for sale as a separate listing.
I have a number of other alnico's I'll be listing soon. Let me know if you've got something specific in mind, like 10" or 15's.