That will be a beautiful collection, especially as you stay within the RED only category. I do collect the earlier issues, but I do not collect just a single designated grade simply because their is very little difference to go to a MS-67 Red on many of the issues.
Likewise, staying with a 66 Red only in the early dates, especially of the San Francisco cents, would jump out of my comfort range rather quickly.
I do go to what I call my "cliff", which simply means if a coin jumps HUGELY in price from one grade to the next, I stay at the Bottom of that cliff. I realize that jump is usually due to very limited numbers having graded in that higher group, but I just can't make myself pay three times the 66 price for a 67.
As for the 51-S, there is a 66R on
ebay with a beginning bid of $25, another Buy it Now for $28.88 including postage, several more in the $30-$60 range, plus a D/S for $75, and MS 67R starting at $100 bid. They list 33 closed recently in 66 or 67 Red, starting at $20.50. So they are there.