I had 3.23's in a 4 spd car and got just over 15 US mpg at 85-90 mph with an 041 cam and ported #48 heads. It was fun watching the speedo needle sweep past 100 mph in third!

I have a 2.56 gear set that is coming out for a set of 4.10's. I don't know the present condition but if you're interested I can have a look.