Why yes, that is a very rare rear XLR head that's going under the knife.
Setting up the plug angle, using the original as a guide. The original degree angle needed to be modified to fit the new plugs without notching/splitting/removing the rocker boxes. It's not much of a variation from perfect symmetry, just enough to clear the rocker box.
The plug holes therefore do not mirror each other exactly, but the difference is minimal.
So there ya go. One note though; seems the cast relative to the head bolt holes varies slightly from head to head, so in this case the XLR rear head gave pretty much the same amount of thread in the new plug hole as in the old one. However, the front head did not. So as not to risk the threads giving up a spacer was placed on top of the threads, silver soldered in place, and threads tapped into it from the inside. That ought to hold it.
Naturally one thing leads to another and now, because of the taller Dytch cylinders, the top rail of the frame will need to be tweaked a bit to get this thing in and out in the future.
Oh yeah, and if anybody has a set of solid mount dogbone risers (taller than the usual 4", and not the ugly square kind you can get from the catalogues), hit me up with pics and price; email@example.com