From a designer's perspective, yeah, the block is going to bring any pump to its knees: you've only got 9 jets. IMO, you would do well to calculate the pressure drop, and try to tune those jets for a pump's optimal range.
Cathar's design compensates for the pressure drop by having a whole bunch of tubes, so it works well with any pump
. As the flow rate increases, the pressure drop increases exponentially, so big pump owners need to have a nice pump, with a lot more head than flow, to run nicely.
I really wouldn't give up on the jet block just yet. LeeJSmith's work is top notch, and uses a brass tube, for the jets, which I think is great because at higher flow speeds, a smooth inner surface in the tube is going to be less restrictive, and should result in a very focused jet.
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Cascade" isn't hard to make, but it's hard to make it right. I think it would be a perfect exercise for you, JD.