In them manual in section 42-155/1, replacement of piston seal on rear axle caliper, it has a list of piston bore sizes but does not mention wagon or not
caliper make- Tevers M 42 (ATE) 41.99/42.00
caliper make- Tevers (ATE), Bendix 37.99/38.03 (the ATE and Bendix pistons have a different shape where the boot attacjes688)
caliper make- Girling, 38.17/38.22

Perhaps the Tevers M 42 (ATE) is the Wagon since ithas the largest piston.

Is the Wagon Master Cylinder different from the sedan?

Did you end up finding the correct rebuild kit for your calipers?
I plugged the centric part number from earlier in this thread in their catalog and it says its for bendix calipers.
I too seem to have girling calipers on my 123 and need to rebuild them.