Drtheo, welcome to the Stovebolt. We have several GMC members here so you should feel right at home. Quite a few bolters from around your area too. Watch for them.
I haven't checked for the parts mentioned but one vendor comes to mind and that is JimCarter. He carries parts for Chevy and GMC....and he also has a basement full of use parts and his outside yard is/was quite extensive at one time. A phone call is all it takes to find out if he can help.
....another way it so post your needs on the Swap Meet area in the PARTS WANTED FORUM.
****but be aware, you cannot send or receive PM's until you have made at least 4 post. So while posting in the forum remember that members will have to contact you within the post, or by email, if its in your profile, until after the 4 needed post are made.
...Chevy and GMC had a few things in common. Could the drums be one of them??
......AND a bolter, Barry Weeks, is a MN. bolter and has some parts. Look him up and give him a call.
