Lifting 200-300 LBS with 2x8 wood - design question
This will most likely work if the body is as light as you say, but that seems like an optimistic estimate.  When you start to lift, the board should tell you if it's going to be ok.

By the book, this isn't strictly "safe", but I don't have a problem with self-engineered solutions.  The one thing you have to remember is to treat the lifted object as if it could fall at any moment.  Never put yourself or one of your limbs under the body and always predict how it will fall if it does and stay out of that path.

What you have created will work, but it is also dangerous in that it has not been tested or properly planned/designed.  It could damage the car, and it could damage you, so treat it like a pending failure, and be happy when everything does work out.