According to my rough calculations I get that the fronts are 42mm offset and the rears are 56mm.
See this site for a good visual reference:
http://www.skulte.com/adapterfaq.htmlA 50mm 17x11 has 7.93" of backspacing. so if yours measures 8 3/16"; that is about 1/4" more or 56mm
A 38mm offset 17x9.5 has 6.7" of backspacing. so yours measures 6 7/8"; that is about 3/16" more or about 42mm.
George E.