Hmmm... The BC-60 had a speaker loosely based on both the Celestion Blue and the Greenback. The JC-series had very neutral speakers (and the 120 is a 2 x 12"), but they are also very different amps so your mileage may vary.
If you can get them, the Electro Voice EVM-12L or JBL D120F would be your best bets - popular upgrade for JC-120 owners (and cleaner Twin players too). Will add some weight to the amp though. Otherwise the Weber California Ceramic (JBL D120F copy) with the aluminium dust cover -
https://taweber.powweb.com/weber/cali12f.htm .