How difficult would it be to turn a ‘92 Toyota Carolla automatic in to an electric conversion?

there are several Yahoo groups to ask if there are others near you.
In the UK the Battey Vehicle Society will help

a good (if a bit dated) guide is

the basic conversion is take out all the infernal combustion bits: engine, fuel tank; cooling systems…
The electric motor is easiest connected to the old clutch plate (electric motors don’t really need clutch or gearbox, it’s just aconvenient point.)
Automatic transmission is not the easiest though, because they are inefficient and have a fluid clutch. You need to find a suitable shaft to connect to afer all the automatic gubbins. Or you could look to go for direct wheel drive. This is more efficient, but requires finding just the right motor. Mitsubushi do this on their 4 wheel drive rally cars, or the Ellica 8 wheeler.

then add control system, batteries, heater, and brake servo pump.
You probably need to adjust the suspension to take acount of the new weight ditribution.

then enjoy smooth, quiet, smell free, low maintenance happy motoring