Adventure Creation Kit - Source
Version info will be indicated by the folder name within the ZIP file. Note that this package contains everything you need to compile the program files (.EXE and .OVR) but does not contain the various data files used by ACK; you'll need a working copy of ACK to drop your new program files into.
To compile: You will not need to download any separate compiler or libraries, just run DosBox, go to the ACKSRC folder, and run "MAKE all" (to compile everything) or "MAKE player" or "MAKE editors" (to compile just those modules). Note that DosBox is required, the compiler is from 1990 and locks up if run directly in Windows.
I highly recommend using the Notepad++ editor for working with the source code.