Probably everyone but me was aware of this, but: I was searching for headers to use on my new to me Class C small block chevy. Went to a chevie van forum and they were discussing this issue. Turns out that some of the headers used on the normal G vans do not work on the cutaway chassis, because there is a frame rail in the way. Normal G vans have a unitized construction where they spot weld the frame to the body, the cutaway has a separate, and beefier frame. Best description as there are some really nasty discussions about frame or no frame on some of those boards. So as a Class C we are different.

Good to be different
Chuckd
Stillwater Mn, brisk -10 this morning, 38th day of below zero am reading. Record is 51.

If you are having trouble with header fitment bring to an exhaust shop. let them look at the clearance problem and reshape the headers to fit. Should cost 50-100 bucks.

Hope that helps
Cheers
Meric