C20 69020 Header fitment issue.

[Sheetaki]

Hey guys, got a bit of an ambitious project I'm working on. I picked up a '67 C20 for cheap, and am in the process of swapping in a much more exciting motor. I bought the 1-3/4 primary Hedman 69020, as they were recommended to me by them, but I ran into a fitment issue on the driver's side. Judging from the pictures on this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=584546
It looks like my truck has a much wider frame than a C10. That would make sense, it's a heavier duty truck, but Hedman insists those headers will fit a C20 just fine.
http://i.imgur.com/pEzsgRU.jpg
If you look at the picture of my frame rail, there's just a ton more metal there than on the picture of the C10. Doesn't help that I opted for the 1-3/4 primaries too....

So I'm wondering if anyone has these headers (or the 69010's) and has successfully fit them on a C20, or if somebody else with a C20 can chime in and let me know that I've got some weirdly wide frame or something. I appreciate any help, I jumped in two feet first blindfolded and am learning as I go .