Two 8 ohm speakers wired in parallel will give you a 4 ohm load, which will get the most power out of the head.
For years I played guitar through Fender Bassman amps. Both original 4x10 combos and 2x12 head and cabinet models. In fact the amp most recorded with by the Beatles was a white Fender Bassman.
Technically, the Kustom K200B amps are designed with modules for the power amp and the preamp sections. The different models have different combinations of modules. That being said, there really isn't much difference in a head that is designed for guitar and one that is meant for bass. Most players don't use reverb and tremolo for bass, so a lot of people consider the Model-1 amps to be bass amps, but they sound great as guitar amps.
The biggest difference that Kustom amps had between models were the types of speakers that people bought to use with them. Most CTS speakers were used in bass cabinets and most Jensen cabinets were used as guitar amps.