Consider a regular car battery weighs around 50 or more pounds. You are going to need several of them. You can use lighter batteries, but will pay more.
The current Prius has 1.8L engine that likely weights in the range of yours. It also has a 100lb battery, alternator, and 2 motor/generators. You thinking of using a system that uses just EV for motive force, so you'll be able to downsize the engine, but that will also mean upsizing the motor.
Have you looked into modifying your existing engine? Guy I went to HS with had a mid 80's Jeep. IIRC, it was an inline 6 with carb, with mileage range from 6 to 20 mpg. A compete engine swap will be cheaper than your original plan. The battery alone will easily cost a $1000. Likely more, and those you can get at Wal-mart.
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