Welcome to the forum and retirement. Building a Gatling gun is a challenging and time consuming project but a very satisfying one. Since you are now retired I suggest you go to the Model Engineering shows were you can see actual guns and talk directly with guys who have been through it. There are three in reasonable driving distance of NEO which I go to. They are the NAMES show in Michigan, The Cabin Fever Show in Penn. and the Mid East Model show in Zanesville which is coming up Oct 17th and 18th. There are always both versions of the GG on display at these shows.
As for building one with a Smithy, you need to check out Dale Detrich who built both the D&E and the RGG using a Smithy 3 in 1 machine. It can be done. His web site is www.daledetrich.com.
You also will want to spend a lot of time at the Gatling gun forum www.gatlinggunforum.com. There is a wealth of information on building both guns as will as custom designs.
I have built both and think the RGG is a much better design if you want a working gun but the D$E is a nicer model. I am located in North Canton, Oh so we must be close. Hope this helps.