Having take delivery of shiny new frame have realised there is no way a 450lbs spring will support my pie-enhanced bulk. I know what weight I need (600lbs according to the TF tuned shock calculator on their website) and I kow it’s a 2 inch stroke but what length is the damn thing? And are there different size of internal diameter to worry about?

yes there are different diameters but a any of the compatible springs (5th, Manitou, DHX) 2.0 stroke spring will fit –
get a Manitou Spring tho, Manitou springs are same diameter as 5th but are £20 rather than £40+

have fun twiddling all the knobs and screws !

True knottie – the manual is fairly intimidating as is the ‘quick’ set up guide on the TF tuned website.