I've recently sold off my pair of 4 ohm cabinets and moved to a single 8 ohm cab...
Here is a cable I custom ordered from "Pro Cables and Sound" to allow a pair of 4 ohm cabinets to be connected to my tube head as a single 8ohm load.
It has a 1/4" connector at the amp side and speakon for each speaker. one 'leg' is 4 foot, the other is 6 foot.
Since I ordered mine, Todd and Patty have offered it as a standard item for $45 new plus shipping
here.
I'll let mine go for $30 shipped.