I think the stock YHD3 are not the flat fabric pads of the YHD1/YHD2 ilk but rather "normal" raised pads but still low profile. I seem to recall seeing that thin foam damping pad in the YHD3 disintegrated in the set I had. I have never had the YHE50 so have no personal reference. My thoughts would echo yours that drivers should be similar. and yes, quite astounding little drivers.
The zebra ID1 are not neutral by any means but they have much more top end than the...
Just an FYI, the carbon is not lush, imo, it is more resolving than the HA-1. ( yes , I have heard both side by side) I like the versatility of the HA-1 and use it mostly as a preamp . It's headphone stage is solid but does not resolve to the same degree as the Cavalli..dB
my recommendation would be to look for CBS/Hytron long bottle 12SN7 - a great tube at a reasonable cost.
I was not a fan of the CV181-Z ShuGuang , the original Mullards were another matter entirely.
no picture, but it is a solid magnet structure which iirc was cut with a water jet . I have been tempted to open them but the possibility of the magnet pulling a screw / screwdriver through the driver has little to no appeal . ( there are stories of this happening during development - hence the need for non magnetic tools ) My curiosity has not risen to levels of insanity yet.