Numismat - I would be very happy to look at any Cap and Ray coin. I have been collecting in the series since roughly 1958 or 59 and started collecting counterfeits about 1960. How do I find it? Is it on a thread?
Regarding the altered date 8Rs, they are full weight silver. There are many
ebay sellers from China who handle real silver coins with altered dates. They do that so that they can honestly say that the coin is guaranteed to be genuine silver. They can also say antique or old or anything similar and it is actually true. The only problem is the date or mint mark. It is a dodge but they get away with it all the time.
Add to that the fact that many novice coin collectors don't have a clue about actual die style variations made from year to year and mint to mint (about 300 total) for Mexican 8Rs and you have a buyer who is not even likely to know he has been swindled.
I tend to agree with your comment that the last 1878 could be an 1876 - all the left side needs some minor trimming and the right needs a small addition, but it is not too difficult for any competent jeweler.