The '54 261 is perfect because you can use the stock water pump. As Tim pointed out, the bellhousing of a '54 mounts differently. Use the '53.

Great find. Go for it.

"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.