Update on x86 extension:
I have refined the implementation of SetThreadErrorMode, (Rtl)TryAcquireSRWLockExclusive and (Rtl)TryAcquireSRWLockShared.
On the x64 side, I've got SetThreadErrorMode and its dependency BaseSetLastNTError. x86 SetThreadErrorMode is based on Windows 2000 extended kernel code, though all others are based on Windows 7 code. Next up is GetCurrentProcessorNumberEx (needed by Pale Moon 28.10.0) and the entire K32* series of functions (there are about 25 of them). And then a few stragglers in user32 and shell32 will be added.
The manual patching instructions will be updated once kernel32.dll is filled out with all of the planned functions.
On another note, I have found a limitation of the DLL redirection scheme. While it works wonderfully for say, kernel32.dll where the program will call the local version, and even other system dlls (not located in the local directory) would refer back to the local version, it appears that ntdll.dll is exempt from it. Mind you I haven't applied the reg key mentioned in the article yet that would allow system-wide DLL redirection.
And as it stands, all program execution (as in GIMP 2.10.8 and a recent version of oCam) using my x86 kernel32/ntdll combo fails ATM. Yes, I did try renaming the local ntdll to ntdl1 then adjusting kernel32's import table accordingly. That still didn't work out as a fault occurred in the main ntdll at 0x77E0F7B3 (RtlInitializeNtUserPfn). I will keep investigating.
update: x86 ntdll is unbootable, but x64 kernel32 still boots to a stable system, now with K32GetProcessMemoryInfo implemented.