Changing crown and pinion in 58 Merc
 

I have a 3.70 to 1 rear end with heavy duty 3 speed tranny ( 4.5 to 1 in 1st gear). I want better millage on the highway so I am considering changing the crown and pinion to a lower ratio. . Will a 2.79 to 1 ratio be OK in 1st and 2nd gear in the city or will I have to slip the clutch to get moving all the time. :-X0A6