Regulators

The left image shows the two Mk1 regulators (both with a small square shaft for the handle) - pull-handle roadster at the top (HZA360/361) with a right-angle curve in the end of the long strut, push-button Mk1 cars (roadster and GT) below with the shallower angle (HZA2118/2119). In the right-hand image a Mk2 regulator (large hex for the handle) with a straight strut (HZA664/665) is shown with a pull-handle regulator: (MG Enthusiast)

The Mk2 regulator has a three-piece strut with two hinge points coming downwards from the handle whereas the others have a two piece with a curve at the bottom in place of the 3rd section. The upper section of the MK2 strut is also longer than the others, and whereas the Mk1 pivot plate uses four bolts with the two-piece strut pivoting in the middle of the plate, the Mk2 three-piece strut pivots in the near one corner replacing one of the bolts. Upper right in the above image, but lower front when installed in the door.

The Mk2 pivot plate mounts to the inner skin using the upper set of holes, with bolts positioned as shown. The later Mk1 pivot plate also uses the upper set of holes, this time with four bolts, so you need to get the plate rotated to the correct position - unknown at this time. Also unknown is where and how the early pivot plate mounts: