I think you're pretty close to your 80 mile range.
Below is a range chart from the Leaf forums. At 60 mph the Leaf gets 82 miles of range. Your DIY setup while very similar to the Leaf likely isn't as efficient due to the DC vs AC drivetrain. I'm not sure what kind of efficiency hit you take here, but my guess would be around 5%. Of course you will gain some efficiency for having a lighter vehicle. I'm also not sure how much of a gain you'll see on the highway though. In town less weight will help a lot more though. If you keep the speed down a little you're golden.
