[Coupeguy2001]

You are measuring to the wrong thing.
You need to get a piece of angle, and put it across the opening. your radiator will not go all the way out to the crossbars.
You will lose a little over an inch if you put something across the opening and measure from that to the fan, but that's where the radiator goes.
In 58-59, chevy put the radiator in one spot,, and used a shroud for the V8 models. The 6 cyl. models just had the fan in thin air.
That way of compensating for the V8 is different than 55-57, in that they installed a V8 kit to mount the radiator 6 inches aft of the 6 cylinder position on those earlier models.
I guess somebody figured out that one radiator position was less assembly on the line, and they could build em faster.