You can connect a jack to the speakers on your Fender Twin, and connect to your 4x10 cabinet from that. The load impedance will drop and power will be distributed across the group of speakers according to their respective impedance values.I suggest that you wire the 4x10 cabinet in series/parallel. This will make the cabinet impedance equal to that of an individual driver. So if there are (4) 8Ω drivers in it, then the total cabinet impedance will also be 8Ω.
The Fender Twin amp has a pair of 8Ω speakers inside, connected in parallel. When you connect a 4x10 cabinet in parallel to the speakers in your Fender Twin, the load impedance of the amplifier will drop from 4Ω to approximately 2.7Ω. That's not too bad, and the amp will be happy with this load.