GMC and Chevy front crossmembers are different. That is where the radiator support mounts. The rest of the front sheet metal is supported by this. Are you sure a GMC front end will bolt to a Chevy crossmember with no modifications?

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.