Heads are off, what should I upgrade?

[westcoaststyle]

Hello everyone. I have a 99 Explorer Sport (OHV) as a second vehicle and the headgasket recently went. In the last couple days I've removed the heads and am going to take them to a machine shop to have them planed and likely do a 3-angle on the valves. I'm not looking for massive performance by any means, but is there anything else that I can do to gain some efficiencies while I'm so far into the motor? What is the most bang-for-the-buck?

Thanks for the help.