[V8] Replacing a 3.6 with a 4.2 - Any BTDT?

[SFevold]

My V8Q is getting a bit tired.  At almost 200k, it's due for a timing belt
service.  It's burning almost a quart every 750 - 1000 miles (good oil
pressure though).  Just about everything else works fine right on down to
the drivers seat heater.  I have access to a low mile 4.2 engine from a 93
V8Q.
I'll probably have a retired Audi mechanic do the work, unless I find a kind
soul who will help me out for beer and\or parts barter.

Has anyone have any experience swapping out a 3.6 for a 4.2?  
Any advice?  
My transmission is functioning fine, it's been running synthetic fluid for
about 50k miles, should I consider a 5spd swap?

Thanks,
Steve