I'm going to convert my '57 one ton to single wheels. I haven't yet found any 19.5's but I'm still looking. I know where I can get some 16's but I know there may be issues with clearance in the front. I've read somewhere that the backspace needs to be checked to make sure they'll work. Can someone tell me what the backspace dimension should be to fit correctly? Any help will be appreciated.

Jeff

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