Robgunbuilder,

I am no expert (or even knowledgeable hobbyist for that matter - just a learner) but I have recently been in touch with Gabrielle Recknagel at Recknagel and she is selling sidelock actions for double rifles as well as Mauser actions built by Johannsen for her company to many different specifications. If you choose not to use the Zabala shotgun action, maybe she would have something for you? I have her contact information if you need it though I am sure that you can afford to forget more about guns and not bother than I will ever learn, and you would likely have her contact information and more.

There are some gunsmiths here including Johann Vilhjalmsson who build double rifles and I shall alert them to this thread and ask them to weigh in with their suggestions.

In any case, please do post pictures of this project as it progresses. This would be an ultimate double rifle, no doubt.

Thanks for bringing this discussion here and good hunting!