Shimano never made an internal battery for 7970. Calfee and a few others made conversion kits, but they were expensive. You could adapt a new E-Tube internal battery, but that's not cheap either. What Teton and I did was make our own. I would be happy to share the details offline. If you don't want to go that route, there are two battery mounts available, long and short. The long goes under a bottle cage, and the short is used for frames with screws in the NDS chainstay. Check your frame for this. I have one of each that I do not need.
As as for wiring you need to decide whether to go internal or external. The internal 7970 harness kit is getting harder to find although your LBS may be able to order one for you direct from Shimano. Both battery mounts can be used with internal wiring. A custom internal battery will have to be adapted but it's not hard if you know how to solder. If you don't I would be glad to do it for you.