To do it right you'll have to replace the floor pan with one from a hydramatic truck. You'll have to cut out some of your firewall. I'm assuming it's like the '54 GMC.

"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.