I've given the exterior a final inspection and it all feels pretty smooth everywhere, so brought the cab inside, ready to redecal.  A pretty good guide on the dry method here http://www.robertwinter.com/pinball/restorations/ft/backbox/index.html

I followed this pretty much (although used the pinball transformer rather than kitty litter for a weight)

Then got scared as i started to peel back the backing paper to stick it to the headbox, so will leave it sit overnight and will convince my wife to give me a hand and some moral support in the morning.

Aligning the decal was not too difficult - just got a bright torch and shine the light from underneath the decal and make sure all the edges have an even overlap.

Here's a pic of it ready to go!