I think you would be far better off building a stroker LA 360 motor for you car than a early poly 318 motor
It will bolt in and hook up to your existing tranny, the only part that won't work is the drivers side stamp steel engine mount, the 340 and 360 are wider on the mounting ears on the block than the 273 and 318 are.
I've seen guys use washers as spacer on their 318 cars, I wouldn't do that but I would use some thick wall tubing as the spacer needed