you can basically tell by looking at them.
if they are twisted in spots, they are stock
if they are shorties (whether stubby or shorty) they are 1 5/8" since i don't believe anyone makes shorties bigger than that.
and if they are long tubes....full length , you can measure the outside to fig it out...it is ID for the sizing but 1 3/4" primaries look HUGE probably about 2 " OD
they are prob 1 5/8" as well though