This is the Dexter 12x2 AL-KO Loaded Backing Plates that you need for the conversion. All of the guts and holes are in the right place , but the actual backing plate is 1/2" too small in diameter to mate with the HADCO hub. This is A RH brake.

With all the parts removed, here is the pivot pin and plate that must be removed and transferred to the HADCO plate. Of course it is spot-welded in place.

A close-up of the back of the Dexter plate showing the ring-weld that must be cutoff and the two alignment pins.

I removed the weld ring using 4 cuts of a high speed cutoff wheel.

I drilled out the two spot welds on the pivot plate with a 3/8" bit. The soft steel drills rather easy.

Here's our removed parts showing the drilled off pivot plate (see the two 3/8" holes) and the pivot pin. These will be welded on our HADCO backing plate to hang the new electric brake hardware.

The front of the HADCO plate with the hardware removed.

The back showing the nut that comes off to remove the pivot pin.

Drilling the alignment holes in the HADCO plate for the Dexter pivot plate. If I had to do this again, I'd have used a 1/4" carbide rotary bit in my high speed to elongate the holes, as they half intersected the old HADCO holes.

The Dexter pivot pin and plate welded in place. The alignment pins of the Dexter plate will align the hardware for welding.

Backside of the HADCO plate showing the welded pivot pin and welds in the alignment hoes for the pivot plate, You can also see the 1/2" hole I drilled for the grommet for the electrical wires.

Reassembled Dexter parts on the HADCO plate. The lower tang on the brake arm has to be reduced by 1/4 inch so that it doesn't stick the magnet too far out into the hub when reinstalled.

Backside of the finished plate, ready for installation.