I see people say they have # 565 or #1257 Indy etc. How do you determine which number Indy you have?

NOT a complete list, but see if your VIN is listed.
https://www.fiero.nl/forum/...L/053812-7.html#p252

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3.4L Supercharged 87 GT and Super Duty 4 Indy #163

I'll offer a comment. Keep in mind that I don't own an Indy, and never have.
It may be a bit difficult to determine what the # is, other than having the VIN entered in a registry.
There is really nothing in the VIN to Identify an Indy as such. They are all simply "VIN'd" (is that a word?) as 84 SEs.
There are some specific RPOs to Identify the Indy pieces, however.