Peter,
perhaps I should have added a final part in full agreement with you. There comes a time, and more frequently so with pre 1960's machines, when through use or abuse ! you can do little else. Of course these are the ones best left to the "experts" (IMO). Hope your successful in your hunt for the correct decals. Nick Tithecott does produce one-off's if you have an original but I'd get in his queue now if that's what your thinking. He produced a 'rare' sized Reynolds '531' decal to my requirements albeit he had the original still on the frame to work from.
I have dimensions and note of two pre- & immediate post WWII styles of box lining that I've seen on other frames if it's of any help, though not in this case used on a Hetch......
Bob Reid Stonehaven Scotland
(still astonished that you've got three 30's Hetchins :-)