The Ritualistic fansite does have the older versions of the source code for the game, though I'm not sure if the 110src applies to to the current updated 1.11 retail version since I haven't had time to compile it, though I did looks through it extensively. I'm sure VS2012/13 can reliably convert the project properties, though this was written in VS5 and those tend to end up either buggy or with some unfixable linker errors. Just cross your fingers and hope for the best.
Haven't tried the level editor yet either, but from what I've heard, it still works with a bit of tweaking. http://ritualistic.chrissstrahl.de/downloads/SIN/utillity/