My classmate last year (mod 1) was diving a 20 year old Kiss Classic he’d bought used from someone who had done restoration work on it. mCCR, so no electronics to worry about. The computer was a Shearwater Predator, no longer supported, but on mCCR the computer is just an O2 monitor. Easy enough for someone to update the sensor head from Fischer to 4 pin connectors for the newest computer (Petrel 3). I even know a few Kiss Classic divers using non-Shearwater computers.