If I remember correctly, AndrewH built a multimast test rig on his benchtop, spacing the masts just as he planned for his hull.
My bottle brig has a better solution (than Pamir) to the boom & gaff jaws construction (for your spanker). Brig uses a loop of brass wire and a serving, in place of the pair of screweyes on Pamir. The new jaws' advantages: Less jamming and less force trying to turn the mast itself. Of course you can make the jaws out of plywood, and be even more realistic (Seaworthysmallships kits). Brass or stainless steel wire would probably stand up to BB's better than plywood, perhaps steel screweyes better yet.