Steering box binding when mounting

Box fits fine until you try to tighten it down. Then the bolts binds up and you can't bolt it down the last 1/2 inch. It's a new Lares 11030 power steering unit for my '68 Charger. ANY help greatly appreciated. Wondering if anyone ran into a similar problem. Car has never been hit, no damaged rail. thanks

Are the bolts threaded down far enough? Bolts hitting rusted threads in the k frame?

with the box out of the way, run the bolts to seat on frame. If not able, start cleaning threads, if able to seat bolts then the new steering box holes might just be off enough to cause binding.