I suspect there is a misunderstanding here. If you have a 210 with two 16 ohm speakers running in series, you just add up and get 32 ohm total, which is imo very unusual. More likely they run in parallelle, which would get you 8 ohm.
If you run a 4 ohm cab in parallelle with 8 ohm, you get a total 2,67 ohm load. A 4 ohm cab parallelle wired with a 32 ohm cab, would get you a total 3,55 ohm.
I wouldn't recommend any of the above, 2,67 ohm will harm most amps. 3,55 ohm is also also a serious risk of harm for most amps.