Towing with a 66 Barracuda with a newer & rebuilt 904

+5 for adding a tranny cooler... I took my '70 Duster with a fresh 360/904 on a 7-hour road trip through the mountains to Telluride, CO and was very glad I added a tranny cooler right before I left. The trans shifted noticeably quicker on the road than with just the factory cooler, no doubt to the much lower fluid temps. Your transmission will thank you, it is a very worthwhile upgrade ESPECIALLY for towing or lots of driving up hills. Also if you ever add a stall converter an auxiliary cooler is crucial to keep it from overheating.

I used one of these, installed it myself too:
http://www.summitracing.com/parts/DER-13504/