Willys pickup - axle ratio
 

Looking at restoring a 60's Willys pickup. In the original state they go pretty slow and it's safe to assume fuel economy is poor.
Anyone have any experience putting a newer engine in and maybe changing axle ratios to gain some speed and economy? Not sure if the original trans is worth keeping either? They make a kit to add a 25% overdrive, it is easy to install and works good from what I read but it costs like a grand or so.
Just trying to make an old truck be a modern cruiser!

Original trans is a T90 3 speed from what I can remember. I like old Willys trucks, but they are made for proper off road use and are geared accordingly. The 4 cylinder is geared to climb hills and trails - slowly. Works great for what it was made for, but the only way you can make use of that for economy purposes is if you are using it around town at low speeds, with lots of stop and go. If you want to actually drive the thing around at highway speed and not have it spinning at super high RPM, look at an eng/trans/transfer case swap. A 4.3L setup from an S10 style Blazer will fit, kits are made to make the swap, and you gain an overdrive transmission along with a much more modern drivetrain.

You could just change the axle ratios to something more FE friendly, but that little 4 cylinder and 3 speed are not going to get along well with it trying to move all that weight around.