Electrofusion, Nicasil and steel liners all use the same style piston and rings.
The later model pistons fit fine but as said leave the lower ring off as the ring pin is exposed into the inlet port.
Don't know about the Rocky pistons but if they are claiming to be for the early models then you should check that the ring pin is in the right place. Easily done by looking into the inlet port with the reed block removed when the piston as at BDC