There is indeed an option for pie menus, it can be found in Preferences - Interface - Use Action Wheel.
I'm unsure whether you'll like it though. It is a complete and i mean a total 100% redo of the original pie menu. It's bigger, it shows sub-menus, it's completely reorganized to feature a logical and consistent layout (to make sure as many options stay in the very same place at all times across all menus). Besides it's the single most crashy feature in the entire Viewer. You can toggle all shitniz and turn the Viewer upside down but the moment you turn on Pie Menu all bets are off, any right click you do (especially those on avatars) can and will absolutely and totally 100% end in a crash at some point, a crash i could never reproduce but i know for a fact is happening (lot's of people already reported right-click crashes with pie menu enabled). Besides it being a big pile of unfun crashes you'd probably like it that is if you got used to the new layout. I'd highly recommend against using it though.
AO was and will always stay a big red flag for me, unless LL gets their ass up and gives us developers a way to properly and directly communicate with the server (specifically with the new server side AO) to replace animations server side i refuse to implement an AO. So much that i have gone up and beyond and scripted my own custom, free, opensource server side AO, it's faster, more reliable, technically never fails unless you make a configuration mistake and works everywhere even when not worn as long as you've at least attached it once every login session, it's also very light and takes up only ~45kb when configured, that's far less than most AO's.
The "Radar" and i assume you mean Firestorm's extensive radar features (because any viewer has a perfectly working one) are just as much a red flag as an AO. I do not support stalking features or those that make it easier to do so, in any way.
The SL camera placement and once again i assume you mean the one found in my Viewer is in no way the default camera at all. Every preset is custom made to offer a selection of usable presets rather than some random values LL got from what was presumably a lucky wheel (like so many things *caugh* depth-of-field *caugh*)
Chat on the other hand can be configured to act almost identical to that of Viewer 1, in any Viewer 2.
Select the local chat tab, click the diagonal arrow to undock it,
put it in the left lower corner below the local chat popups
go to preferences and enable the "hide on focus loss" and "hide on send chat" options to make chat pop up when you hit enter and vanish again when you send chat,
collapse it to a single chatbar and you essentially get the same as before,
just the chat popups are not going across the entire screen and IM's remain separated for organization purposes both of which i think were the worst features of V1 chat (besides the entire V1 chat in general being tabbed as it is now once again.... ugh). I do share your hate for the "Conversations" window, it is almost always on screen and is simply annoying but i'm sure the same was true in Viewer 1 (which is one of many reasons i hated it)
About the Viewer using the V2/3 UI. That's just how it is. I'm happy the V1 is gone. It was limited, it was big, it was clunky, it looked dirty (as in not clean) and it wasn't in any way more practical than the V2 UI now, mostly because V1 and V2 UI are almost identical still, mostly it's skin was changed, everything else has been basically reverted to what it was again after everyone complained about the Sidebar, including the "new" chat which is just the old chat with a new name-tag on it...after people complained about a perfectly fine and much better chat system than in any MMO i've seen so far. Even though i hate saying this but i've reverted some parts of the UI as well mostly just to reduce the abnormal spacing LL has put between each UI widget for whatever reason.... *caugh* Windlight editors *caugh*
I do hope though you'll find the poser useful, i'm going to add even more stuff to it soon including (hopefully) being able to pose animesh, everything else is a secret for now ooooohh mysteryyyyyy...