The Keeley uses two delays in series.  That usually means you have to use the Filter Pong algorithm in an H9.  I wasn’t satisfied with the ‘rhythm’ it created.  I suspect the cross-FEEDBACK path(s) differ from Filter Pong.

All is not lost.  I got roughly the same ‘Halo’ results in many of the other parallel delay algorithms.  (As an aside, the UltraTap *pedal* format – with FEEDBACK – seemed perfect for this application).

It will take some fine-tuning, but I was getting good results with Spacetime, MultiTap, even PitchFuzz (no ‘fuzz’ & arp delays).  Tape Echo, if the Keeley saturation is important to you.  Vintage Delay for the bucket brigade mode, etc.

It’s all in the feedback looping path, & diffusion on the repeats (SLUR-M).  I was working those almost with 2 FEEDBACK alternatives.

Other than that, the examples I’ve heard are cascading dotted eighths & quarter notes.  375 ms. and 500 ms. at 120 BPM.