I was thinking I'd leave the rudder servo placement as late as possible in the assembly, so that I can see what works out best for balance, but could be that the 46AX just won't be heavy enough to warrant placing it on the tail.

I already have the four stroke in question. It's several years old and has been used very little. Just didn't end up using it when I got it originally. To be on safe side I should replace the bearings in it since it's been sitting unused for so long and possibly corroding the bearings... hence why I'm using the 46AX initially. I'll probably need help from someone when doing the maintenance on the 4 stroke.