On Coppercoins, as best I can tell by the photos, is that the best potential match MIGHT be #23. But the coin in my hand, the primary "D" seems more tilted than #23.
https://coppercoins.com/lincoln/dies...&die_state=mds
What do you think?

Looking at the RPM below, the overall look, seems to have this RPM slightly tilted to the right. Most of the ones on Coppercoins seem to be tilted to the left
Other RPM's that are close - but no cigar are:
17, 20, 21 and 25.
I have five of these RPM's in hand. I looked over each of these coins to see if any of the die markers existed that were on Copperoins, and none of them are. I am a little concerned that this RPM is not #23, as the look of the split upper serif appears to be different.
OK, now that the best info I can offer is out there, have a look at what I see under the 'scope:
1964-D unknown RPM-x2.jpg
1964-D unknown RPM-x4.jpg
1964-D unknown RPM-x8.jpg
Since I have 5 of these, I was able to find some common markers on all five of the coins. There were others, but these seem to be the more pronounced ones:
1964-D unknown RPM-scratches-BER-x4.jpg
1964-D unknown RPM-scratches-date-x4b.jpg
Have a look, help and ask any questions about this coin. I don't have a definite attribution for this coin - yet.

1964-D unknown RPM Obv.jpg
1964-D unknown RPM Rev.jpg
Comment