I am converting my tub/shower combo to just a shower. What kind of shower head assembly would I use?

What kind of faucet do you have now ? Is it a single handle ? 3-stem ?

If you plan on having only single shower head than you can get shower only valve body. You install shower head riser with rough-in. If you plan on having 2, or 3 shower heads, than you will need additional diverter valve.

You are not mentioning anything about drain. That's usually where lots of questions are asked. How did you figure to relocate the drain ?

Please, come back with specifics...