Compiling this code for anything but a 68k Macintosh is a pretty tall order. Between Quickdraw and MacPaint over half of it is dense 68000 assembly language, and both the assembly and Pascal code makes raw calls to parts of the Mac OS and ROM APIs that we *don't* have the source code for. Porting this to a modern platform would mean translating all the assembly code to either x86 assembly or C (commercial tools exist to help with either, but the end result would need a lot of massaging to be at all useful), porting the archaic Pascal to something that works on a currently available compiler, fixing all the internal calls, and writing replacements for the Mac API elements not included. (Or patching the original code to use the modern OS's native API instead.)
On the bright side the assembly language seems to be pretty well commented. The Pascal... not so much.