rally wheel decode help

[stssilverado]

Just picked up a set of wheels from a local guy. he said they were 15 x 8 off of his chevelle. however, the codes read FW. I'm finding that FW wheels are 15 x 7 with .30+ offset used on 70-72 monte carlos. I measured the backspace and it's 4.25". Can anyone verify this info?

Will I have a prob using these on my 68 camaro conv? I realize tire size will be an issue. What diameter tire would most be like stock?