The 6G has better ventilation and larger fans = runs cooler compared to Ford's earlier versions. Cooler running means a more reliable output. The 6G is also supposed to be more stable under load.3Gs are good, but had heat failures when used in extreme apps, such as limos and public service vehicles. The 6G was the fix for these problems.
Comparing the standard non-highout units..
The large case 6G puts out 90ish amps at idle. The large case 3G puts outs 75ish.
The small case 6G puts out 70ish, the small case 3G puts out 60ish.
If you're comparing apples to apples, the 6g is the clear winner.
I'm thinking that Most year full size broncos used the 180* mount?? << If that's right, the large case 6Gs are a hard find for that app, so your choices are the 3G or small case 6G.