-12 would push the wheel/tire out more.
While offset and backspacing basically measure the same thing, at the same time they are very different. Offset measures the distance between the wheel center and the mounting surface and backspace measures the distance between the mounting face and the inside edge.
Offset = Measured Backspace – Calculated Wheel Center Distance
Found this chart:
Wheel Specs | Wheel Specialists, Inc.
The 0 OS and 5 BS 9” wide tire should stick out a little more than mine. Same 0 OS with a wider wheel.
I’m not an expert on this stuff. I know you want steel wheels, but... my old stock steel wheels were 7” wide I believe (could have been 8 though) with 245 tires. You might go with a taller tire on stock steel wheels. I’m sure there are many in junk/salvage yards. Otherwise a stock 17” might make sense as shadetreevanman mentioned. You could see if the 255s will work on a 7” wide wheel.