Barn, that's looking awesome! You've done a really good job and you're a good couple of months ahead of me getting mine on the road.
I may be able to help with the flares and extensions. I have factory flares from my K3500 and extensions from ED-NY. Looking at them I think it will be possible to mould GRP replicas, it's really just a case of how 'factory' and 'nice' you'd want them, in terms of if I mould the extensions without some of the fixing brackets and returns of plastic then it will be much much easier, but you may need to make a little alu bracket to mount them, or have an exposed fastener. Also if you were happy to paint them then I'd have far less prep work to make them nice. Let me know if you're interested by reply or PM.