It's way too late for me to be up drinking tea and looking through pages of pictures on class31.co.uk, but I am!
To carry on with this mess I need to figure out what I have – I simply don't know. Having looked at the site above, there seems to be quite a few differences between 31s. The two most obvious body differences that can pin down this particular loco's destiny are steps behind one of the cab doors (I don't have any so it can't be one of those variants) and the exhaust outlets. Mine are two oblong holes, where many are single round holes of various dimensions and styles. I'm guessing these could be later models and/or engine upgrades.
So, before I continue, what are my options in regards to prototype? I can't see a definitive description of the various guises of 31s anywhere so I'm stumped.
I'm home alone again tomorrow night (tonight actually, it's 2.10am!) so I can start soldering the grills back in that fell out while unsoldering it. Perhaps also cutting some angle brass for strengthening the body sides too, and taking out those over-scale grab handles on the roof.
A small footnote. I was going to complete this for pulling my Mk1 Suburbans but as I have now sold them on, this requirement no longer exists and will probably open up more options, which I hope is a good thing. This also applies to livery – I'm no longer fussed about what colour it is.