This is something that would be accomplished under Experimental Exhibition. FSDO can help you with the legalities of that. Not a difficult change to make.

However, I am not aware of any existing kits. You would have to contact the manufacturer of one of the electric motors and controllers that are being experimented with and start designing with them. Not my cup of tea, so can't help much in that arena. But look at one of the light sport planes that is touting electric power and go from there.

To me, it seems a criminal thing to do to a classic aircraft.

-Cub Builder