Replacing crank shaft washer

Ok, not sure if this is where I need to post this but need some advice from you experts!
Putting on a new nose cone to my MDS40 and find that with the prop, nose cone and domed washer, there is very little thread left on the crank shaft to screw the holding nut onto. The domed washer which holds the prop to the back plate is about 5mm thick which seems very exessive to me. I just want to know if there would be any issues in swapping the domed washer for a sturdy flat washer, and the nut, to a locking nut?
ie in order it would be - plane, back plate, prop, nose cone, washer, lock nut
Doing this would give me a bit more crank shaft thread to play with and I would be much happier with the fit!
Cheers all
Ben......

Ok, don't shout, just seen this should have probably gone in the 'engine' forum! Sorry!

Yes that will be fine just make sure the the washer is the same size just
to spread the load.

Roy