Your stock crossmember will most likely be in the way. It was putting the 200-4r behind my 248 in my '54 GMC. I used the CPP crossmember. You will have to drill bolt holes which ever one you use.
To see the problems I ran into click "Transmission" when you get here.

"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.