In my 1981 Malibu wagon I used a Pontiac 400 and Saginaw 4 speed with the 3:11 first gear, 3:23 rear. I have to say that was just about the ideal set up. That gave me the perfect 10 to 1 overall ratio. Easy take-off and highway speed was OK too. The 3:11 and 3:89 rears would be 12 to 1 overall and way too steep. The ST-10 with the 2:43 and 3:89 rear gives you a much better 9.5 to 1 but top end highway speed will suffer with that rear. But you must know that already. I think for just cruising around the ST-10 is your better choice.