In addition to what JiMerit said, you'll need to use the '48 bell housing. The mounts are different. Also, the starter and flywheel must match. If your system is 6V use the starter and flywheel from the '48. If it's 12V use them from the '58.

"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.