Glad I could help.
It was easy once my wife and I were on the same page. I rolled around on the creeper measuring, and she wrote the #s down. I had a sheet with the bunks drawn as lines and an area at the front, middle and rear of each with A and B lines for #s. I just told her where I was and said what the reading was. She held the paper down under the boat for the first few measurments to make sure we were in sync.
My only concern is that your crossmembers may be at a different angle than factory, and then the "B" measurements I gave you would be off for your build.
Let me know if you need another measurement or check. I'm here with the boat/trailer.