Back half question

[Zero Clearance]

Hi ladies and gents. Im working on my 65 c10 and had the bright idea to back half it. So I bought some 2x4 and got to welding. Anyways as life gets busy with work, family and my baby 65 c10, my attention cant always be spent on playing with my baby and the back half project got stretched out a little. I have an idea where its supposed to be but Before i start welding i just need someone to give me a measurement from behind the cab from the floor to the top of the rail and the very rear from the floor to the top of the frame rail. I have every other measurement but the one i need and want confirm before i tackle it and end up cursing and throwing my tools lol. I just cant seem to find it. If anybody can do me a solid id greatly appreciate it.

Almost forgot. 65 c10 swb