Mexico, 2 Real, Overstrike?

Just back from auction with a box of jingles and this one has me stumped.
This is not at all my area of expertise, but I'm always willing to learn.

Diameter is 1.1" or 28 mm.
Weight is 90.7 grains or 5.88 grams.

Obverse appears to be Carlos III (overstamp?) With a date of 1788?
Reverse appears like Mexico with variant markings.

My question is what have I got?
Is it an overstrike?
What was the donor coin?

Thanks in advance.

Still working on this but this is what I believe to be the base coin from Peru (or possibly KM76a) I cant account for the weight and diameter differences but that could be attributed to crude minting or simple wear.
https://en.numista.com/catalogue/pieces26018.html

Your coin is a 2 reale coin from Peru (IJ mint-mark).

I agree.
But it looks as though it was struck over something else.
Maybe it was a double strike or mint error, but the Peruvian version is 6.7668 gm compared to 5.88 gm.
Is a 13% loss reasonable for a worn coin?