Old Pixhawk and 4.1

All my copters are running cubes, but I’ve got a pile of old original Pixhawks. Currently building a boat, are there any limitations to the old Pixhawk running 4.1 rover?

Pretty much anything will run a Rover. But here are the limitations if it’s a 1Mb version of the Pixhawk:
https://ardupilot.org/copter/docs/common-limited-firmware.html#common-limited-firmware