The only difference ithe distortion and sustain controls, and a footswitch to operate them. The 880 was described in the catalogs as an option for both bass and guitar, and offered at the same time as the Coliseum Bass and Coliseum Lead.
Although all three are included in the '72 catalog, the Bass and Lead were introduced earlier - both are in my late 1970 product pamphlet.
When I bought my Sorado in June 1971 at Quigley Music in Kansas City, a Coliseum Bass stack was right next to it in the showroom. The guy at the store said it was the first one they had received from Sunn.