Thanks for the response Bob much appreciated, that's kinda what I'm thinking but also looking to reuse as much as possible to minimise cost as much as possible given the NZ$ ~= US$0.65...

It also seems my actual questions didn't make my original post (my copy and paste must've failed me)...
1) Can the EM components be (easily) transferred to my EF, essentially to create an EE that could then become a secondary display with an AF5xxxx as primary, with the ethernet cable between them as with the AF3500s?? Any issues with that as it'd save me some $$ if I could??
2) Can I reuse the existing AFS engine, OAT, manifold, etc sensors with AF5xxxx screens?
3) Can I reuse the existing TruTrak autopilot servos if I were to install an AFS autopilot?
4) I've been thinking of using Garmin transponder/ADSB as they're certified and NZCAA are currently making that a requirement for entry into controlled airspace. I do want ADSB-IN with info displayed on the AF5xxxx. Any issues with that?
5) What else do I need to be aware of?? (the ultimate catch all

Bob mentioned a tradein/credit on my AF3500s, what's the value of that?