The old MDS assembler is used to assemble and link the files, however the code is real straight forward, without a lot of globals and such, so it should be simple to translate this to any other assembler.
To assemble the programs, place all of the above files on the startup disk, not in any folder. Then, in the Finder, select the four .asm files and Open them by either double clicking or from the File menu. Repeat this with the two .link files. After the commotion stops, the files PocketForth0.5 and PocketDA will be on the disk. Throw away the.rel and .map files. If you make changes and get errors, you are on your own.