I'm building a prostreet 69 valiant and need some advice on engine placement or location. It has a front and mid plate. There's no k frame or anythingsuspension its eventually gonna have a bobs pro fab. What's the best and easiest way to locate the motor up and down and front to back. The engine is centered in the car

Install all your accessories and headers as well as oil pan and pump.Place the engine so that you have sufficient clearences.In most instances set the engine as low and as far back as possible.

Stock floors, firewall, rear trans mount? If not...

The driveline should run parallel to the centerline of the car front to rear. If the pinion is offset, then the engine/trans should be moved to match it or fix the rear. "Down" is determined by the oil pan and/or the K frame and/or the ride height. "Back" is determined by the firewall. Pay attention to the angle up or down of the engine/trans assembly from front to rear. It should be parallel to the pinion or very close. Too high in the front in a car that sits low, can result in some real driveline angle issues. Don't forget, someone has to make headers fit. The farther you get from stock location, the more custom everything becomes and the more attention you have to give to how it relates to everything else in the car.

I used the tranny mount to locate it for/aft and then centered it up in the bay before welding in the motor plate ears.