We dont want uniform serifs in this design. Wed lose too much of the rough, irregular look of the original. The baseline should be straight, however. (Trust me: I tried random bumps.)
Heres a systematic approach to accidental results.
The black serif on the right rises twice as high as the black serif on the left. It is also a third longer. These two are our starting points. First well make three variations from the the left one.
The first variation is twice as high. The second has a slightly curved slant. And the third has both the curved slant and twice the height.
Two variations on the second starting point are enough. One has a slightly curved slant. The other serif has it, too, and is shorter as well.
Put together, these variarions are all we need for a random effect. But you can add more if you like.