wow this thread is all messed up,,
17.5 and 16.5 and 16 and 19.5 are all found on gm since the 60s and before through the 80s
i ahve had many 17.5 rim 67-72 duallies they are common as dirt and 19.5 were available
the 71 dually i ahve nopw has 16" splits on it
16.5 existed all the same years too
there were no certain years except that 17.5 and 19.5 died after 72
17.5 were std equipment base rims 72 older years
they were not 17
just for an example, here is straight from 68 chevy truck specs books printed by chevrolet in may 1 1968 series C20 for dealers to show buyers ordering options for a new vehicle purchase/order:
standard equipment;
wheels;
five 17.5" x 5.25"; attachement, 8 studs on 6 1/2" circle; spare carrier under frame; four painted hubcaps are used
on 68 C-20 series trucks these wheel sizes were optional equipment:
tubeless:
16.5" x 6.75" RPO QE7
16.5" x 8/25" RPO S89
tube type:
16" x 6.00" RPO Q20
i have other years too, and tires and all kinds of other original gm std and optional equipment RPO info
good luck