I've been using US post and Canada post with good results for the last 10 years or so. Couriers are way too expensive.
At this point I'm not ready to take on any more work.
I did look into it a few years ago but at that time there was very little interest. If I were going to put together the kind of head pkg that I do for the other stuff I work on, there would be a bunch of work involved like porting and flowing the heads, quality parts sourcing, and cam profile development. It's not fair to expect a few customers to pay for the development, and not feasible for me to do for small volumes, when I have other stuff waiting on the bench.
Maybe in the future, but not right now.