ok, here's my 2 cents.
I am in the process sticking an AOD into my 55. I'm still not done, however because I have got in to all kinds of other rebuilding issues all over the car such as interior and front end etc. And of course I never have any time to work on it, it seems!
BUT I made my decision on the AOD BECAUSE if you have to buy an adapter regardless and do other changes, why not go the AOD (essentially the same cost overall) get an additional gear, better gear selection and rear gear options.
Main considerations are:
Do you plan to run the stock shifter, you can but it will take some mods, I was able to get all 4 gears manually selected with my stock shifter.
You will have to trim the X Member (not much) in the frame and probably make a new tranny cross member, alter the drive shaft length and a new yoke.
And of course change the throttle linkage/kickdown, like to something such as LoKar.
With either swap there is more to it than most will tell you and depends on how much of a hotrodder you are.
There is a good article on here in the old Forums on the c4 swap.
When and IF I ever get back to work on it, I'll have a full report. Maybe this year-Columbus.
A L A N F R A K E S ~ Tulsa, OK