I was told by a transmission shop to look for a hex indent in the top. These include stronger parts. I don't think they started 'til the late '80's though. Mine came from an '89 Cougar. If I was to do it all over I would have put in a 5 speed manual or go the extra with the Hi$ interface module and install an AOD-E. I don't like the shift characteristics/pattern of the AOD other than Full throttle.
if you already have the AOD, go ahead and swap it in place, it will do fine for even a mildly modified small block. if you have a choice though, go for the latest model AOD before the AOD-E came out as those will have the most upgrades. check out http://www.lentechautomatics.com/index2.htm for good information on upgrading the AOD, and installing it in earlier cars.