Cutting out floor to replace Floor Hump

[76PasoGMC]

Ok I am using a donor cab from a 2wd 3/4 ton C20 to replace the cab on my GMC K15. The cabs are identical except the floor hump. The one in there is a small hump 2wd. I have to put the hump out of my old cab as it is a 4spd/4X4 hump. The one in the donor cab is not bolted in like my 4X4 one. So my question is, can I just lay my "tall" hump over the floor in the correct area, mark out the holes and drill em. I was then thinking of bolting it down then tack welding the nuts on the underside. Then I can remove the bolts and the "tall" hump THEN cut out the floor.

What do u guys think??

Thanks

Tony