I suppose in a way my naivety is quite touching, but I really shouldn't have been surprised when my plan to make one master for the sides of the FR and WHHR Hudson toast rack carriages hit a snag.
A correspondent informed me that there is a clear difference in the pair in the orientation of the upright L girders on the sides.
While the WHHR rebuild has them as per the original carriages the FR replica - built by Winson Engineering in the 1990s - has most of them facing in the opposite direction.
I am also informed that this is not what was designed, however, that is what was delivered!
Armed with this unfortunate information my options were:
a) build separate masters for the two carriages
b) try to slice off the uprights to make a generic master to which I could use to cast incomplete sides and add the uprights separately for each carriage.
I've decided to go for the second option.