So in the front an 18x9 +24 should fit with a 255/40/18 as long as you stay with the 73+ mopar disks. That combo should be about a 1/4” inside of the 275/35/18’s I run on my car. I have 18x9’s with a +35 offset, but I run 13” disks that widen the track 5mm and I’ve run a 3mm spacer so that’s effectively a +27. I don’t think you’d clear 275’s but 255’s should work. With 18” rims the tie rods fit inside the lip of the rim, unlike a 17”.
In the back, what year is the B-body rear? It makes a difference. Also, are your springs in the stock location? I have a 68-70 B rear with 1/2” offset springs, my 18x10s are a +38 though with 295’s.
***Edit***
In the front you will most likely have to either have the wheels machined to enlarge the hub bore or have the hubs on the rotors turned down some to clear the wheels. I had my enkei’s machined to clear the hubs on my rotors.