Cab mount to bumpstop measurement needed - Help!

[sighlurr]

I tried searching for this measurement, and couldn't find anything.

I've welded in the original holes for the factory rear axle bumpstop brackets, and now need to know where there were. Oops. I'm converting a '70 leaf to coilovers and need some help with finding the rear axle center point on the frame.

Can anyone tell me what the measurement is from he back of the rear cab mount, to the center point of the bumpstop?

Multiple replies are appreciated as I'd like to make sure I've got the right number before I start cutting for the notch.

Thanks in advance for your help!