Inconsistencies between my Nortons and Thevenins equivalent circuits
For Rth while calculating you have gone wrong.

1 ohm and 50 ohms come in series which together come parallel to 27 ohms.

So,
RTh = 51 || 27 = 17.65 ohms

Vth = 12/78 * 27 = 4.15 volts.

Now in Nortons theorem,

When you short the load the  27 ohm also is effectively removed.

Isc = 12/51 =0.235 amps.

Rth = 17.65 ohms.

Isc x Rth = 4.15 which is our VTh.