For you getting harmattan working in 0510 hw revision would be quite hard, as you would need to find old enough flash image with 0521 xloaders, or R&D signed flash images. Most likely its easier for you to use nemo or sailfish, unless you happen to have good sources to old images or R&D images. Or if you get your hands on the N950 phoenix flasher/serial-console/external charger docking station (they are quite rare).