ZZP solid mounts aren't solid, they just have no air bubbles inside so you can't hear it when you shake it. If you drill them out, most "solid" mounts for that matter, you will still have hydraulic fluid come out.
Either run the hydraulic ones, or if you really want a solid mount/more reliable mount, just get the cheapest you can find and drill them out. Get as much fluid out as possible, and then fill them with black RTV and let them cure. Being that you're doing this soon I think, maybe just run the hydraulics and drill them later when you have time to let them cure? They'll squeeze out the RTV if they haven't cured long enough.
The whole solid rubber mount situation sucks, I've gotten so many "solid" mounts, only to find fluid in every one. Either I'm buying the wrong ones, or they're hard to come across.
That was the write up I saw a while back as well,it said basically everything you just did.
I guess finding a completely solid mount is like seeing a unicorn drinking a beer...lol!...extremely hard to find like you said.
'01 GTP: Rebuilt Trans by Andrew S....300m,hardened 4th,Transgo shift kit,V8 chain ect ect,3.8 MPS,ZZP 10.5.....More to come!