55.2-59 gmc who has added heat and possibly a/c

[dsraven]

I think ogre has done a lot of really nice fiberglass interior work in his truck.
With the GMC curved dash you could possibly make a straight run to the curved section and then zig and zag over to the column area. Make a pattern out of wood and bend some lighter gauge cold rolled flat sheet around that. Curl the edges over with a mallet or another piece of wood and a hammer. Or hammer on dolly. It doesnt need to have a large lip to screw it to the dash or on the lower edge either. If you have an hvac shop nearby that has a break for forming ductwork they may be able to make you a channel shaped section cheap enough. Or a fab shop could easily make what you need. Lighter metal is easier to work with but will also gets damaged easier to. 18ga would hold up well and also be sturdy for drilling and screwing the vents in. When you make a vent hole it will weaken the structure in that area.