1961 Ford Fairlane high rpm's @ moderate speed

I have a 58 fairlane with a 3 spd on the tree,no overdrive,it seems to me that the rear end ratio is to low,raps out @ 3500 + 60mph or so,i want to get a more hyway gear ratio to put in it or a overdrive unit?seems to be the origanal unit,I've looked @that part--help!!