Last year I picked up three mounting brackets, three sockets, and three "jeep style" gun cradle for my project from Al Steifel in Oroville. This is the cheapest and easiest way to mount your .30 calibers. Two months ago I decided to go with one 1917 water cooled, and therefore I had to change the cradle for that weapon.
I am selling one of the cradles for what I paid - $150. Plus shipping. Shoot me a message if you need one. The pins do not have the retaining ball installed. You will still need to track down a travel lock, socket and bracket