Unless you have the time for it, I'd skip the running for more riding. 2 x 20min threshold efforts on the road bike will do wonders for your cx fitness. My schedule looks like this...
M - off
T - 2x20' road bike
W - CX endurance ride (trails)
T - Hard group ride (road) or CX training race
F - off
Sat - 3hr group ride (road) or CX race during season
Sun - CX practice or CX race during season