Is it the OG Casa? If so that used the RPi3 which would still work but is pretty weak. I just converted our old Casa node to an Umbrel node to test out that software stack.
If you're interested at all I can write up a post for building a Raspiblitz. I think you'd be able to go from the parts you have but worse comes to worse you might want to pick up another RPi4 ($55) to replace the board on the Casa.
That would be cool. and yea I think it is the OG Casa, had it for a couple of years now. I've heard some great things about Umbrel, how do you like it?
It's extremely user friendly but has known security considerations while still in development. Once they are all addressed then I'll really like their system.