A 60E or 65E CAN be a good transmission IF built right, but finding a builder is the problem. I have a 60E in my 9 sec Camaro and in my 12 sec nitrous truck...all has been good with my build. I will agree the 80e is a better trans but they do have their fair share of problems as well. It depends on how hard you will be on it and your end goals and if you trust a local builder.

As far as your 4.3L 60E I bet its near the end of its life if its a stock unit and hasn't been build. If you can get a good working 65E that will be a great start , them come with 5 pinion planets from the start and hardened output/input depending on years...

If you stick with the 60E I can send you a build list if you need and post up more info on the entire setup if you will