I'm getting ready to install a B & M trans cooler and the instruction say you have to hook the pressure and return lines a certain way. Gives you a list of transmissions and which line is pressure and return, except the 4L60E isn't in the list.
So, is top radiator line pressure and bottom return or vise versa.

 

Top line is return, I went with the fact that 4L60E is basically a 700R4 with electronic controls and used the top line as return.
I cut off the crimped hose with a tubing cutter and hooked it up there, did not have to use the brass couplings that way and the install looks alot cleaner. I don,t have AC and took the condenser out so I had lots o room and the little bracket on the bottom of the radiator that held the line for the condenser works great to hold your rubber line for the cooler.

 

Here's a pretty good guide if you need it. It's not a B&M, but it's the same idea.

http://www.bfranker.badz28.com/94z/trannycooler.htm