Ok so I've done the usual think on it overnight (always works quite well)

So if I were not able to get hold of 6x10 in fresh cut doug fir, could I then go for normal off the shelf KD 2x10 (like you said) with the eased edges like you get with normal carcassing then glue them together to make up the 6x10 would that be viable? I dont want to see metal fasteners, so could I just glue laminate them then buzz through some 5 1/2 screws from the back side?

And would this pose any issue working with fresh cut wood, fresh cut braces but KD beams? I take it as the beams are already dry I just cut the tenons a little short so they can shrink a little?

Thanks!

Elliott