Maybe you should try
this.
It is for use with EQ2 mount (via additional gear stage, I believe 1:5 or close) and rotational speed is such that when driving 144 tooth worm gear, you end up with sideral rate.
Now, obviously the rotational speed is not 1r/min, it is 2 rot/min (if that additional gear reduction is indeed 1:5, - I am not sure, but someone may be able to confirm), so this only means your barndoor arm must be shorter (or you should use adequate, finer threaded rod).