I owned a pair of Premier 12s for several years and had a chance to compare them to the ARC VT100 mk2 and CJ Premier 140. Ran them with the GE 6550As they were originally voiced with along with an RCA double-mica black plate 5751 and military issue Sylvania 6FQ7s. The 12s are excellent representatives of the 'old world' pre-21st Century CJ house sound.
As you note, they are 'full', which I take to mean harmonically rich and a touch warm - definitely to the yin side of things. Nice bass extension though not quite as crisp on low end transients as say the VT100, yet to my ears, harmonically much more pleasing. Very good sound stage width and depth with reasonable interior dimensionality on woodwinds, choristers, etc. Not quite as resolving and not quite the punch of the Premier 140 nonetheless quite satisfying over all.
Modern day they will do fine with the Svetlana 6550C and RCA clear top 6CG7/6FQ7s. Stock they do not have an IEC plug, but they most certainly benefit from a simple rewire to a decent mid-range power cord such as a Shunyata Diamondback which will really tighten up the bass and yield better overall resolution.
Tim