15G is a good upgrade from an ease point of view, if you get one with the same downpipe fitting (conical) - they need clocking to fit but have a less restrictive exhaust housing.
240ratrod - if your 240 already has a 4 speed autobox (which the internet suggests you would at '84) then it's the 'same' as the 940 box and keeping that for the cable drive is definitely the easiest option. Look into removing the overdrive solenoid and keep on top of the fluid to make it works properly. Shame you're up in Notts as I'd say pop round for a demo otherwise
