Cuckoo filters for non powers-of-2
Yes, it is possible.  Use

$$h_2(x) = \text{hash}(\text{signature}) - h_1(x) \bmod n.$$

The theory behind this: if $c$ is a constant, the function

$$f(t) = c - t \bmod n$$

is an involution for any $c$ and any $n$, since

$$f(f(t) = c - (c-t) = t \pmod n.$$

Therefore, we can use the hash of the signature as the constant $c$.  This gives you a scheme that works for any $n$, without requiring that $n$ be a power of two.