1980 Spitfire towing 101:
1: Get used to doing it, it'll happen a lot
2: No need to disconnect the driveshaft on a dolly, unless someone has managed to find an auto box that'll fit. If in doubt, tow it backwards.
3: Whilst it is a good idea for the tow vehicle to be heavier than the towed vehicle (on unbraked trailers) for a Spitfire, any decent sized motorcycle will qualify (or for that matter a bicycle ridden by a fat guy)
4: If you tow at night, this is a good way to tell if you have a flat on the vehicle being towed - due to the shower of sparks visible in the rear view mirror. This is a good thing as it has saved you all that work cutting the rust back to good metal, although in the case of many late Spitfires, this could mean you are now grinding an empty tow dolly.
5: get rid of those ridiculous US market bumpers as soon as possible, it'll halve the weight of the car.
As you may tell, I'm not a big fan of late triumphs, the late 70's was not a stellar time for british car manufacturers and anything that came out of British Leyland factories at that time (Austin, Mini, Rover, MG, Triumph, Jaguar, Land Rover) was poor quality with some very odd design. On the other hand, the Triumph Spitfire is an awesome little fun car and if you're willing to put in the time to bring it up to a good standard, they're great. Just don't stop at "showroom standard".