before i start pulling hubs apart just to try, does anyone know if i can fit a 9sp shimano freehub on a circa 1990 shimano 105 hub that currently has a 7sp cassette/freehub (i have checked and there is no spacer on the cassette so it is the pre 8sp hub freehub)?

as i understand i will have to re dish the wheel but thats not a bother.

Many moons ago I’ve done such a thing. Freehub will go on but axle will need re-spacing to make space and therefore a redish is needed.