C++ isn't my main language so don't quote me on this but afaik if you take 1.5.5's VC6 project folders and just place them with the FLSAC stuff then all u should need to do is include HkFLSAC.cpp into the project. I only have Visual Studio 2003 which is VC7. I don't have any clue how to actualy make VC6 project files with VC7(If its even possible).
Note: You can get the original VC6 headers for 1.5.5 Here.