You need to explicitly pass in the params to the overlay. I think this should work in houdini.nix:
self: super:
{
houdini = super.houdini.overrideAttrs (old: rec {
name = "houdini-runtime-${version}";
version = "17.5.229";
src = super.requireFile {
name = "houdini-${version}-linux_x86_64_gcc6.3.tar.gz";
sha256 = "b20e0f35c51479fe3f89489ad64122b96f9d14eab26b54dbc062fdbb1681f5e0";
};
});
}