sounds great clapthom, im the same situation as you... sucky that nintendo never made a GBM->GC cable even though they did the GBM->GBA/SP one =(
But dont hesitate to contact me once you have it figured and and have the time to make me one :D!
Are there still people willing to assist with the creation of a cable ^? Im from sweden and would prefer if you could order the cable on your own, have some solder-fun and ship em to me. This with payment before you order ofc.. and i hope i dont get scammed if i find a helpful soul here =)