forgot I had this

For some reason, I just remembered I had this. Bought it for $34 probably 30 years ago. Has tons of data plate info in it as well.
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I have one as well. Had it maybe 20 some years.

U so Lucky!

Was a bit green so wondering what it would cost to get one. Seems $100 is about right https://www.amazon.com/Interchange-Systems-1963-1974-Products-Manual/dp/B003XA2FUM

But in this digital age is something like this available online?

Mustang is well supported for spares. Having a source of cross-over part numbers would sure help in the quest for parts.

Most of this info is probably available online now.

Here is what I use. Was used by some wrecking yards back in the day. Includes part numbers, interchange numbers and prices
you would expect to pay at a wrecking yard. Includes all makes and models as well (trucks too)
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One would think so being as useful as it is… but where?

Neat! How thick are they? Mine is only about 1/2" thick.