Coach built 63 - help id'ing builder

[BK]

Hey guys, exciting news for me. I found a 63 2 door crew cab and am picking it up Friday! The owner thinks it was a Canadian GM built crew cab crew cab for CM railway but I know gm didn't build them themselves. Here are some specifics which may help narrow the builder down as I haven't found a tag anywhere.

The frame has been z'ed near the end of the cab. Chassis has 4 wheel power drums.

Bed length looks to be a longbed that has maybe 2 feet out of the front.

Crew cab length looks to be the longer of the ones I've seen.

Floor does not kick up behind rear seats indicating a panel or suburban, but floor had rubber covering.

Roof has taller crown in rear like the rear portion of a truck roof or rear of suburban roof, but has odd trim or seam at kick up.

Ceiling ribs of rear headliner go opposite ribs in front.

Anyway, here's a bunch of pictures. I looked quite a bit for a tag from a builder but found nothing besides the no spin Eaton badge on the dash.