1972 Camaro 18" Fikse wheels, HELP!!!

[NastyZ]

Hey guys, I'm new to Lateral G! You guys are all awesome and im hoping you can help!

I have a 72 Camaro Z28, It has been dropped 2" all around. Mild set up, CPP control arms, lowered springs and lowered leafs in the back.
I am rolling the rear fenders and plan on beating the seat belt hump with a BFH.
I ordered some Fikse Profil 5S wheels and they showed up yesterday and dont fit!

I got sent: Front 18x8.5 with 6.5 backspace
Rear 18x10 with 6.5 backspace
This didnt seem right, but he said thats what he has done for other camaro's that year....... Anyways they are going to be send back. My question is will 18x10 with 5.5 backspace in the rear and 18x8 with 4.5 backspace fit well?

I have read that 5.75 backspace on rear 10" rim is what I need but they only make then in 1/2"....

Any input would be great! thanks guys!!