It's a total of 3.5A rating indeed for the power transformer.
The relative currents don't really matter.
A 6080 tube runs @ 2.5A heater current.
So that's 1A to spare for the driver tube (the driver tubes for Crack i know of don't exceed 0.8A).
Using 2 6BL7's (6BX7) in parallel (2x 1.5A) you can use up to 0.5A for the driver tube.