Need wheel help ASAP for 2004 prerunner

My son has a 2004 prerunner reg. cab that came with the 15" steel wheels. He wants some new wheels and I have been trying to order some for Christmas. Each time I think I have this figured out and order some I get a call back saying they may not fit. He has new tires so I wanted to stay with 15" wheel and was looking to go to a 15 x 8.
I thought this size was good Offset: -19mm Backspacing: 3.74" Bolt Pattern: 6-139
They are aluminum.
Does anyone have first hand real world experience? What offset and back space is correct?

Thanks for the help. Im running out of time.

 

Yes its a 6 lug. It came with a 15 x 7 steel wheel and P225 75R15 tires. The sticker in the door frame confirms the same.

 

What size tires is he planning on running?

Stock backspacing for '04's is 4.5"

 

31 x 10.50 x 15 Tire