Captodaport, I bought and just installed my rearend swap kit from
www.classicperform.com It had the spring perches and centered up the rearend to appx. 27" centerline from bothends of the spring. This should work on '47 thru '55-1st
The kit also came with new shock mounts to convert from knee-action to tube but also order the lower shouckmount bolt(unless you have some) because the "KIT" didnt come with it. Good Luck!
bowties