As I'm boxing my heads up to send out to Len for a rebuild, I pulled the vent tubes for each head. They came out real easy and I got me thinking that they may be a source of future oil leaks. The hole seem the perfect diameter for my 1/4 NPT tap. I'm thinking of tapping them and threading in some brass vents with thread sealant. Does this sound reasonable?

Heads we have worked on from Raby's Aircooled Technology were tapped with 1/4" NPT.
Fittings with 1/4"NPT x 1/2" hose barb are hard to find but we have some from McMaster.
Its a pretty tight fit in that area of the engine, with the intake manifold right next to the vent.
I personally like a 1/2" smooth tube, JB welded into the head. For this reason, and since a lot of heads have no vent from the factory, I recently started including a length of 1/2" aluminum tube with our Breather Can Kits.