Hi Trevor,
I fitted a 2 axis DRO to my Warco 1327 lathe (same as a BH900) last year, and found it surprisingly easy.
I fitted the cross slide scale to the right of the carriage so that it didn't interfere with the headstock end. It does obscure the carriage lock a bit, but it's easy enough to extend the screw and fit a bar to it.
All in it took me about 5 hours to fit, and I don't rush!
Andy