I had the same problem. Its hard to get something in the running board support to get to those nuts. Plus they are all rusted. I got mine loose enough to were I could get my sawsall blade in between the running board and the support and cut the bolt. Have to be very carefull not to damage the running board. Those bolts slide into the running board they slide in from the middle of the running board to the to the out side. So.. if you can get the ones closest to the cab loose you may can pull the running board away from the cab and pull it off leaving the bolts in the support. did I confuse you? You can also fine I think a six point socket to fit that square nut but will need a deep one which is hard to find but there nothing holding the bolt wont do any good any way. Seem like I had every tool in my arsanal out trying to get mine off. Just have to work each bolt whith wat you have to get them off. Good luck.

"Finish the thing, do it right the first time, and drive the S.O.B.!"

1949 Chevy half ton 3100 In a kazillion pieces
2000 GMC Serria 1500 SL 4x4