Rear tire height clearance 69 dart

mopowers said
Measure the clearance you've got with the tires on it now. The first place it'll hit height-wise is the front edge of the wheel opening. Measure the diameter of the tires you have on it now as well and compare that to the size of the tires you want to buy. Then do the math. That'll give you an idea of whether or not they'll fit. Every car is slightly different, so measuring your car will be only only way to tell 100%. If it's a tad too tight, you can always shim the front spring hanger as needed.

The problem is that I cant measure anything as I have no access to the car but need to get the parts ordered. I know each car is a bit different but its not an extreme size so Im hoping someone has some experience.

I should have mentioned this, 225/50/18 tires that I would like to install are the exact same height as the 215/75/14 tires I am running. However the shape of the two tires is totally different, the ones I want to get are modern with a much larger contact patch.
If you took a cross section of the old tires they are an oval shape whereas the new ones are square like. The new tires are around 225 wide throughout their height while the current tires are 215 at only one point half way up the side wall meaning less clearance. Hope Im making sense, not sure how to explain this.