I agree with Shaun, A 74-75 auto prefered for the 2x main reasons, 1, bigger tunnel to install most gearboxes, inc Celica without reshaping tunnel;, 2, rear shockers are more vertical, ie mk2 style.
I have noticed that the later models got more spotwelds along the chassis and engine compartment/ strut towers etc.
My car is a 72 auto shell which had 45deg inclined rear shocks, i fitted turrets so the shock problem was eliminated, as well i seam welded the shell to GP4 standards.
If you find a late 75 model the chassis code will be CK44 RSxxxxxxx, handy if doing an RS replica !