i chose the easy route...
sand blasted first, then started to hammer the louvers down and realized it was warping the cover.
i just used duraglass (short strand fiberglass filler) and smucked up both sides.
welded in the ends, seam sealed the top edge (windshield edge) and bottom edge.
finished with regular filler. not much to it, really.
when i had my cab blasted i asked the blaster to get inside the cowl and made sure primer covered everything inside.
plus i covered everything in there with undercoating from a can.
i've seen other builds where the louvers were cut out and metal welded in.
not sure which one is better, just telling you what i did and what my body/painter friend told me to do.