If the best mpg you can get in a prius is 60 with pg, then you must have the parking brake depressed 5 clicks.
Just fill the tires to sidewall psi and you should get 65mpg plus keeping up with traffic.
The prius is a whale of a car when it comes to the other eco vehicle of early 2000. THe gen 1 insight is slightly smaller than a 3 door geo metro.I doubt you can get all the crap under the hood of a prius under the hood of a gen 1 insight.
Now if you just want to use the engine, theres a guy here who put a prius engine in another toy, but the engine alone isnt what leads to the fuel economy of that car.