I just made 1" extension's out of aluminum square stock and matched up S/S allen head bolt 1" longer then the stock ones from a local hardware. I had the 1" longer S/S bolt's with locking nut's for the rear on the primary side at the house already.
I hope you checked for the grade of bolt you bought or you could get a big surprise.
Generally the bolts in the hardware store aren't a higher grade like used on these bikes. The SS bolts are also graded differently too.
Most hardware stores i visit sell grade 5 and 8. Unless your fatter than a sumo wrestler i doubt you would need a grade 8
Here is a handy thread chart
Thread Pitch Chart | Portland Bolt