You can mix and match quite a bit with the Hammer bodies and lead heads. For the 7" bait, I would go with either 3/4, 1oz or 1.5oz. Use the 5/0 or 6/0 hook versions. You can see what is available on this page:
http://www.swimbait.com/hammerhead.htm
For example, if you're fishing shallow grass areas, you could put the 3/4oz head on and get more float from the bait. If you're dragging down deep you can put on the 1.5oz and get it down there pronto. Adjusting what pound test line you use can also affect your depth control. So for the shallow grass area fishing, you might want to go with 25lb to really keep the bait up. For the deep bite, use the heavier head and go with 17 or 20lb test to get it down. Hope that helps.