I think you should shoot for around the same ratio with a four speed if you are going for MPG. You could go lower numerically but you might find yourself dragging the clutch a little to get started.

Saginaws have fairly low first gears compared to a close ratio Muncie. A Saginaw out of a 6 cylinder car has an even lower first gear. With a 3.36 to 3.42 ratio, these transmissions will quickly get you off the line compared to a closer ratio manual transmission. If you do go lower numericaly, shoot for a first gear ratio of a high 2.00. (Like a 6 cyl trans) V8 Saginaws are around 2.50 first gears.

I had 3.36's with a Saginaw in my 307 69 Camaro it was just right. Decent acceleration with OK mileage.