26 uppercase, 26 lowercase, 10 digits, 12 punctuation/space = 74.
No, the digit keys all have special characters when you hold shift, and the 11 special character keys all have 2 choices as well, so there are 33 special characters on the keyboard including space. That's 95 total. Look at your keyboard and count them.
I think this throws off the rest of your calculations. The 43 numbers and punctuation together are a lot more than the 26 lowercase letters. And you failed to take into account that, even when done in a stupid way, people are likely to switch around the order somewhat (uppercase at the beginning OR end of the letters, and number/punctuation in either order, and sometimes even at the beginning instead of the end), which adds a few factors of 2 at least. Even one number and one punctuation in either order is about equivalent to two lowercase letters, but better because they help reduce dictionary words. I'm with you on explicit requirements of numbers and numbers only.
But yeah, you're better off either encouraging but not requiring some punctuation and numbers, or having looser requirements like the common "at least 1 each of 3 of the following types: upper, lower, numbers, punctuation", plus some restrictions on sequences, dictionary words, etc. It's probably a good idea to require something like at least 6 non-numbers for an 8-character-minimum password too, to keep 7-number plus 1-letter passwords from getting too popular. But if you're coming up with your own password solution (like just about everyone with the type of requirements you describe), or copying one from a non-expert, then you're probably doing it wrong.