I think the issue was related to the fact the fuel and temp gauges hadn't been used since 1995. Might have been stuck, not sure...
Anyway, I wired them up for the first time on Sunday (one of the last few jobs needed before it's on the road) and they didn't move at all. Earthed the sender out on the temp circuit, no movement, dash started smoking, needle then shot up all the way to the top and the voltage stabiliser and a little relay on the PCB at the back of the dash burned out.
Got the dash out quick, unplugged the wiring, my mate "helped" me remove it by unclipping the speedo cable whilst pushing the dash toward me. BANG, nice little dent on my forehead and dash removed.
I've found an immaculate second hand one on eBay for £30, plus I've got a mate that's given me a freeby for now.
MOT should be on Monday, hopefully.