One thing comes to mind after re-reading this thread and looking at the I 28's keel profile. You might want the supports to be a touch heftier than 2x4's, just in case. )(4x4?) Adding a chock
or a notch to the upper end of the support so that it fits in a specific spot on the hull might be a good idea too - you don't want the thing slipping too much out of place, once you get it in. The engine & tankage weight aft would make me want a strut back there too, if only to protect the rudder.