after taking apart an AGR box this summer and discovering that all they were doing was taping and rebuilding stock castings anyway - i wouldnt hesitate to just tap and re-build my own box... or tap and re-build a large piston "Durango" box...
The cooler is necessary IMO and well worth while. Every time i go wheeling, i hear my stock power steering system complain and whine from heating up fluid and the fluid thinning out... and wince a little... A cooler and (probably) some higher quality fluid in my system would cure this...