Some advice

You MAY be headed for a world of disappointment.
Highway gears and choppy idle dont play that well together.The path you are going down needs almost extreme attention to parts selection. If you are married to highway gears,tall tires, and the 904, you will need the 360 for sure, and a shortish period cam.Concentrate on keeping port velocity up, and maximizing compression for the available fuel.
IMO, do not be misled by horsepower numbers. Concentrate on building torque and let the hp fall were it may.You will have a much funner car.
There is no better feeling IMO than rolling on the throttle at sub-2000 rpm in second gear, and hearing the tires scream for mercy.First they whimper. Then they moan, and wail, and scream in agony. Thats torque.If you dont have torque, you will need more cubic inches or torque multiplication. And that leads to more gears in the tranny.
But WTH do I know.