Still looking to replace J/P, K/P and M/P with solids. Also would be nice to find something more special for the replacements.
Yes yes keep upgrading your set. Don’t stop until you have:
The Ultimate 1967 Centennial Prefix and Serial Number Collection of All Time!I think for that you’re going to need to find the solid serial numbers 1111111 & 5555555.
You already started the millions, you have to finish them up or at least find the 1,000,000.
You already have a number 1 but you need the opposite too, you need a 10,000,000.
Maybe an ascending ladder 1234567.
Maybe a few nice radars for replacements upgrades.
If you like specimens then there are two of those.
Don’t forget the double date 1867 1967 serial number. A simple one but your ultimate set isn’t complete without it.

You probably have the best 1967 set there is but it’s fun to think about what the ultimate set of all time might be.