PCE has very simple code, and unlike Basilisk II, doesn't make use of threads (which Emscripten didn't support at the time). Basilisk II also uses a SIGSEGV handler to catch invalid memory accesses, this would have to be coded around. I'd still like to port Basilisk II, which is feasible now due to new browser APIs, but it's a big project.

The Macintosh ROM is up to the website (e.g. archive.org) to provide, along with the disk images.