Since my last post I've done quite a bit to the car. I ended up getting brand new headlight retaining panels from the Triumph Dolomite Club. At £35 each, it was an absolute no-brainer and when I came to fit them I was vindicated because the remants were staring to rot. I changed the engine oil, oil filter, air filters and spark plugs. All the lights have been fitted and they're fully working. I've also fitted the bumpers and the front grilles. I also replaced all 4 tyres. Replacement dust covers for the top balljoints were sourced from the TDC.
One problem I had to address was the hazard lights. The car is a mixture of early 1850 and 1850HL and had the later type push/pull hazard switch. I had fitted the early type dashboard and the early type hazard switch (which is just a big rocker switch) needed to be wired up. With the help of a guide to diagnosing indicator problems (found in the Dolly Wiki), I was able to get my head round it. I tested the various connections for voltage and continuity as and where necessary and then I connected everything up and it is fully working.
Just need to get that MoT booked...