For the Goth RG65 MXP (designed by Frank Russell, built by MX Components) the mast steps are tubes that extend near to the bottom of the hull. The forward tube is 9mm diameter and, of course, is intended for the swing rig. The aft tube is 9.8mm diameter at the base and increases to 10.0 x 13.7mm at the deck. The latter allows the mast to be raked.
I can easily design and build a mast ram that will attach to the keel bolt (M3 screw about 39mm aft of the mast tube). I know that a mast ram is normally attached forward of the mast and is pushing against the leading edge. In this case, the ram would connect to the mast using a ring so it could pull, rather than push, on the mast. (Whether I need a ram or not is still an open question. The point is I can add a ram later if I want.)
My mast is 7.95mm diameter at the base (ground to fit the 8.0mm ID of the SailsEtc 012RG or Breaking Winds ball bearing gooseneck). My current thinking is to make a small ring that fits to the base of the mast. The purpose of that ring will be to hold the position of the base inside the mast tube, and yet allow the mast to be raked (and even allow small adjustments laterally).
Then I plan to use shrouds (0.27mm = 0.0105in stainless steel wire, American Fishing Wire #02, 12kg = 27lb test, available on Amazon.com). M2 rigging screws will be used to attached the shrouds to the MXP’s chainplates (already installed – thanks, Maurizio!). I’m working on the means for attachment to the mast; I would prefer to terminate the shrouds at the masthead crane and hope to avoid the need to drill holes in the mast. (By running the shrouds up to the masthead I keep the mast loaded fully in compression. By avoiding holes in the mast I minimize the chance of creating a weak spot and a mast failure.)
The deciding factor was Marc’s comment above:
If you go shroud-less, your mast tube alignment and placement must be perfect.
The flexibility I get (as far as rig tuning) seems to outweigh the complexity and added wind resistance. I am very comfortable with performing rig swaps on a boat with shrouds; after all, most RC boats do use at least one set of shrouds!
Thanks for the suggestions, guys!