you can make a "multiplayer SDK" yourself by deleting some files from the SP SDK. Here's a hint: if the copyright notice of a file says "This file contains proprietary and confidential information of Valve" or something then it's a SP only file, just delete it. and if it's "this file can only be used for non-commercial purpose" it's a common file
I made my MP patch by copying files from the SP folder into the MP folder, but only the ones that are common. Anyway, does your patch make the DMC source code, Ricochet source code and all the source code under the utils folder compile under Dev C++?
Could you, at least, Whistler tell me what code and how you changed it to compile in Dev C++? I know that different compilers compile slightly different codes.