He is using a Gitzo Explorer tripod and Markins M10 ballhead. He want to be able to set the ballhead in the normal position (like it would on a normal tripod)but with the explorers arm set in the horizontal position.
Once a while i do have request for custom parts. Same parts are easy to make some much more complicated. If you need a part not listed in my auctions I can usually make it. All I need is some input from you. It takes time to design and machine part. Anodizing process required another week or two. Please expect 45-60 days for such project.
If you want to know how much will it cost I have to know what will need to be done. With your input we can design new part. After that i can give you complete quote. In most cases product can also work for other costumers and I can produce more than one part. In that case you are charge only for product you are buying and not custom work. In most cases we are looking at $50-100 for plates, rails etc. If you need custom setup supporting for example Lecica M8 with 800mm lens with teleconverter and your rail need to be 24 inch long I may charge you $300.