A 1965 Mexico TR is a very desirable radio. Also a very odd radio to have in a W110 190, as it is rather top-of-the-line in a rather not top-of-the-line car. Did your father's car also have the neck roll style headrests?

I'm assuming it is the pinstripe small-face radio with the smaller profile (as would fit in a W110 that year). Part of the value is in the condition. If the chrome surround is in good condition that's a big deal. If it works, that matters too. If the search tuning works, that matters. It really depends on condition.

It would help a lot if you sent or posted pictures.

The value depends on the above, and verification that you have what I think you have. It's a radio for high-end cars, so the owners of those cars tend to have lots of money so it is worth more than maybe it should be. I would say right now you have a pretty big window ranging from about $500 to about $1300.