IMHO you don't have to assume anything if you want to use a tune on an actual C64 program, initialize everything you need. Or is this compo for .sid files only? I don't think so.
Any chance for 256b category as well? ;)
Tips If you are a musician who is not a coder, you probably know someone who is and would be willing to help you. If you really don't, you can at least enter the 2k category with a tune in a slim player such as GoatTracker or NinjaTracker.
I don't know about other coders, but one feels he's wasted a valuable amount of hours/days for nothing.