Thanks Andy. This is a job I always put off, but it's not that bad if you're in the right frame of mind and have the right materials at hand. I've found a pic of 6430 pulling 2 autocoaches in 1964 at Yeovil, clearly showing the pipe. It's in 'The Western since 1948' (Ian Allan).
Job done, using Araldite (I know it's overkill but it's not stringy and very controllable), a pair of no. 7 tweezers, a matchstick (for mixing the glue), a pin (to apply the glue to the fixing holes), some IPA (a good solvent for wet Araldite) and a bright light. I fitted the coupling hook as supplied to the loco front , as I'm not using a front coupling, but cut off the dummy coupling for the back hook as I'll fit a short Nemcoup later.