On mine the centerline of the hole is about 3-1/4" to the bottom of the plate.
My set are quite old.
https://calvertracing.com/product/mt-2-mount/
Information on line states the distance should be enough so that the rod should be able to miss the springs by at least 1".
If it doesn't, these lower brackets will need to be a little longer.
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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 )
Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/
Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
Best time 5.13 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE