I think the 3800 springs are wider than 3100. I don't know about 3600. This link may have some helpful info. https://dl.dropboxusercontent.com/u/30524403/1957-3800-rear-springs.pdf



'64 swb stepside (gone)
'57 1 ton
'53 phone truck
'59 swb
'46 1 1/2 ton
'68 swb gmc