yep I hear you on the MPCC, I used it with the TSOAG9 for a while and it just snuck in. the RCC should do the trick, to make up the space TS have adjustable spacers that might be worth looking into
I like this one as it has the M48 thread rather the narrower T2 options.
http://www.teleskop-express.de/shop/...-17-23-mm.html
With your 'frac if you are guiding on the newt with an OAG at the same time you won't need the OAG in the 'frac imaging train? Im also considering putting a small refractor (or camera lens) on top of my newt so interested to hear what options you end up with.
cheers