Also according to GM's Vintage Vehicle Services,
7588 1ET67 - 2SS - convertibles where built in the model year.
My wife requested this information for me as an Christmas gift.
I can tell you the Top color is noted as 67T so that could mean 7588 Beige Topped
convertibles where made but I cant tell you if they are IBM or if they are all 2SS.
I am going to call on monday and request more info.