At last!
3.1 Rom turned up today and now the 600 hard drive works like a charm. Prior to rom fitting, after I cut pin 1 it worked after a reset so I it was a spin-up problem.
After having my first 'real' go on the 600 today I'm suprised at just how damn slow it is. Funny how my impression of speed has changed so much in the last 10+ years, I always remembered them (well, my 500) being reasonably zippy!
Wonder what a zx81 'feels' like now? gonna dig it out the loft tomorrow and give it a go!
cheers for suggestions all