I don't know what year truck you have but on my '57 3800 the front fenders are the same as 1/2 and 3/4 ton. Actually, all the sheet metal from the cab forward is the same.

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