Sorted! I'd guess it took me 20 mins start to finish to get a functioning 27sp set up!All done using original double shifters, front and rear mechs and bottom bracket.
The triple went on fine: the 9sp front mech / shifter would shift from the granny to middle ring and back no problem, but even fully adjusting the top stop screw wouldn't give me the big ring.... all it took was a slight rotation of the band on mech and..... BINGO
So... all I changed in the end was the chainset, and I'd say I'm 95% of the way there. The small ring will only work with the biggest four sprockets until the excess chain fouls the rear mech: Removing a link or two would solve that, but It'd be too tight on the big ring.
I'd guess a long cage mech would sort it 100% ?, so I might keep an eye out for a good priced used one. It's not a major hassle as it is, tbh all I wanted was a bail out gear for really steep hills / touring, and that's what I've got. All I've got to do is remember not to shift to the granny ring from the smaller rear sprockets.