I'm not so sure. I wouldn't go hooking up 24V unless you get an answer from someone at IFI who knows exactly what you have and what it's specs are I remember there were two separate websites and possibly separate divisions of the company. There was IFI Robotics which served the combat robot community and there was Innovation FIRST which served FRC. I believe there were two different Victor 883s as well.
This page seems to show that the FRC Victor 883s are not suitable for 24V use.
this datasheet seems to confirm that. (Oh how wonderful the almighty Wayback Machine is) Additionally, these FRC Victor 883s are only rated for 30A continuous where the combat ones are rated for 60A continuous.
Now, it is possible that IFI/Innovation FIRST is lying and they are actually both the same 24V 60A model because they didn't want combat builders to get special pricing for FIRST so they tell us ours is 12V 30A, but I think it is more likely that they are indeed different units with different specifications.
Note: the 24V Victor 883 can be seen
here on the old IFIRobotics website and note that the 12V one linked to above is on the old InnovationFIRST website.
So,
Do not run your Victor 883s at 24V, at least not until we find out for sure.
Also,
Here's an alternative to 24V victors which is a bit cheaper (but it has no case or fan). It is two speed controls in one and can work on 4-36V and handle 50A continuous (per motor).