Hi. I installed an Eaton HO72 with 4.10 gears and "No-Spin" in my 1949 Chevy 3600 3/4-ton. I understand the Eaton HO52 and HO72 are identical except that the HO72 also has a thrust bearing adjustment(?). I'm not familiar with the '57 trucks, but if it's an Eaton HO52/72, you should have no problem.
If nothing else, the "No-Spin" option on the Eaton rearend is worth the risk. All of the 4x4 guys on the '67 to '72 Chevy Trucks web site are looking for the "No Spin" opion.
Good Luck!
Dan M.
