I built a cradle the heads sit on so they are very close the the spray nozzles in the jet cleaner.
When laying on the rack in the bottom they don't really get the full pressure to blast off the crap.
I always dis-assemble before cleaning so the under spring areas get the full blast pressure as well.
Then flip the head for the chamber.
I use the very strong oakite turbo det powder and that seems to work very well and takes manual labour to a minimum. I tried a local shops US cleaner a few times thinking the same thing but for the cost it was no very good at making the heads look new again,
For the out side I use cast iron chips from the boring machines and brake machine in a blast cabinet, I only do the chamber and out side of the heads this way and blow the heads off before washing to avoid plugging any holes.
It does not imbed like glass beads do and is way faster then glass as well.

Soda blasting mat be a better way if you have a large volume of head work as it dissolves in the jet washer but does not remove heavy gooey crud well of fast enough to be a time saver.