Here are the instructions for building the Tiger I gearboxes (fits King Tiger, Tiger KV-1/2 and Panther):
http://mrdesigngearboxes.webs.com/manualtigeri.htm

The only thing your going to be cutting are the shafts, and brass spacing, I did the cutting with a hacksaw and vise. You'll need a to notch the shafts for the allen screws (you see them in the pics). It's real easy...the first time I did it I was afraid of screwing up but it turned out great!

Regards,
Duane