Hammer ya just get rid of him it want be worth the hassle and all the crap he will try to put on you.
I get stuff like this all the time .
If he would have called diamond they would have told him the right comp.hgt from the part no#
I just went thru about the same thing last week with a guy that wanted a 11.1 piston the shop that was doing the work on his engine called and gave me the part no# for a je/srp piston witch says's it is 11.6 so he started throwing a fit that it wasn't what he wanted.
I told him thats what the machine shop ordered and with the piston being down in the hole it was 11.1 be he sent them back because they 11.6
tried to tell him that they are measured at zero deck but i just refunded his money and went on.
No need to try to please them all Cant be done.