I use the ole tape messure my self If its got a 3" ID than use if its a 2.5" ID sale it Just focus on the 3" part and you will be ok
I went down and bought a reman VAM and the part store had the same part number down for a SVO and 88' TC. I'm guessing one part number is a 2.5" ID while the other part number is the 3" ID.
O and sorry about the typo on the TC's Stinger cought