72 Suburban 3rd row seat measurment needed

[2tontruck]

My 72 only had 2 rows and I am adding a third row in the mix. I need to know how far back to put it . I have a general idea but I am going to fabricate a under the floor cross member and I would like to keep it close to the original area. cam somebody please take a few measurements from the start of the wood floor so I get and idea? Any help would be great! Thanks!