Tough spot to be in...
I remeasured cuz I was a little tired this morning... Without a doubt 25.5" on mine. Again, my engine is not in the truck and I got an actual measurement with straight frame horns. 2" further back and my engine would have hit the firewall...
There was a pretty wide tolerance from the factory on these weldments, but I think 2" is excessive even for the 70s...