i guess ill return them, much easier than playing with rates. its not like im auto x'ing it

The only issue in terms of improper proportioning between front and rear would be if the W126 has larger pistons.

If I had to guess........from memory........I'd say that they were the same size. The W126 piston is not very large and I cannot imagine that the W123 is smaller.

It may be that the only change in the caliper is the width between the piston faces.

Get a hold of a W126 caliper and compare them. You might find that it's not an issue.

brembo rotors for the front are offered.. they are solid .. so it is basicly paying for the name.. but the parts house.. did in fact recive an order for W123 brembos and sent the W126 brembos instead...