Hi John;
Iain Oughtred sent me a drawing of a birlinn that never got built, but apart from the general appearance I didn't use it. I did some very rough sketches, which I cut up to make temporary bulkheads for planking the shell, built inverted.; the ribs were inserted later. So no real drawings I am afraid- you will not be far off if you crib a Viking hull and add a stern rudder.
I think I posted quite a few pics of my build sequence; most of the details came from Google searches.
Dennis Rixon's book "The West Highland Galley" has no drawings, only photos of grave slabs and other early depictions, although the dust cover has a pic of the modern replica Aileach. That replica is not very accurate; best ignored!
All the best, and good luck modelling,
Phil Siddall