I did some more searching on site on the 71-73 coil springs, and ran into this post
http://www.fordpinto.com/index.php?topic=7218.msg42906#msg42906 by Oldkayaker, and got more confused, he states other free lengths for 71-73 and 74-80 coil springs.
Time to call in the professionals, I emailed the following text to EATON Detroit spring;
Dear Sir or Madam,
I'm writing this because there seems to be no information on the Internet about the proper suspension measurements of 71-73 Ford Pinto's.
There is ton's of information on 74-80 Pinto's, and out of ignorance, lot's of people are installing 74-80 coil springs into earlier Pinto's. I believe that is completely wrong and even outright dangerous.
There is a growing active community interested in all sorts of Pinto's, look for instance at fordpinto.com. My project is presented there under the name 72DutchWagon.
It would be in the interest of all of the community if a reputed company like yours could may'be take a look at your manufacturer blue prints and come up with the correct (and safe!) unweighted coil spring height numbers for 71-73 Ford Pinto's.
I'm not asking to reveal any trade secrets, but a few numbers would help a lot of us Pinto fans to be more aware of the differences between 71-73 Pinto's and 74-80 Pinto's.
I will of course make sure that a topic on fordpinto.com will be adressing this issue.
Thanks in advance for your cooperation, if this is not possible than thanks for your time reading this mail.
And got this answer;
Geert,
Very good request. The 71-73 Pinto front coil springs are much lighter springs than the 74- and up springs.
While the ID's are pretty much the same, the wire diameter is smaller and the spring rates are lighter and free height is less for the 71-73 springs vs. later years.
Depending on what 74 - 78 spring was used on a 71-73 Pinto the front would raise between 1.75 inches to as much as 3-inches over factory height.
Our part number for the 71-72 without factory air conditioning is MC1706. With factory a/c the part number is MC522.
For all 1973 Pinto's our part number is MC522.
I hope this helps everyone on the forum. Now who else do you know who we can help?
Thank You
Mike