you should think about adding an extra 0 to the wattage ratings of those speakers. as has already been said, bass frequencies require a great deal more power to produce than guitar frequencies, so while 30W speakers may work great for your guitar, if you use them with a bass you will get very poor response, and are very likely to blow the drivers.
also, if the cab is wired for 16 ohms, you will get very little power from your bass head, and probably won't be loud enough for gigs and possibly rehearsals. I would suggest either wiring it for 4 ohms, or using 8 ohm speakers so you can add another cab later if you need/want it.