The flat spot on the face is the nozzle is there to smooth the filament down as it extrudes. You generally extrude wider than the filament nozzle, so you need the flat area to smooth the extrusion down properly.

I think you'd need to get something machined if you want to use your new nozzles. Either that or put some form of insulation inbetween the heater block and the heatsink - you might get a few more mm if you can insulate it.