It relies on "shuffling and inverting" multiple delay signals as an alternative form of an allpass, but I can't really understand how to variously invert multiples of a single delayed signal. Am I better off looking to the more standard allpass examples in the documentation H.15.phasor and passing the multiple delayed signals through this?

There's also two matrixes referenced, the Hadamard and the Household, and wondered if anyone had any tips on how they work, what it might look like in PD...are the matrixes combinations of additions and subtractions of signals, like in the rev2~ reverb example?

Actually I came across this reverb whilst looking, like you are, for a way to do the calculations.
In Pd extended there existed [lowshelf] [highshelf] and [equalizer] as externals in the ggee library to do the same more efficiently.
They have been available again for a while for 64-bit Pd... but they were AWOL for a couple of years during the 32>>64bit change.

You will need [lp8_cheb~]..... another filter... for the patch to run in vanilla.
You should be able to find it in the iemlib library, and other parts of that library...... [filter~] for example...... are required for that to create properly.
David.