I can only comment on the surrounds, I have never replaced the cap too. I've tried two different methods. One involving a 9 volt battery and one without. The toughest job I had was redoing a pair of 15" woofers in an old pair of Heathkit's. The problem is that once you remove the surround material, the outer edge of the cone sits lower then the metal basket. So what do you do? I found one suggestion online of connecting a 9 volt battery to the terminals so that the diaphragm would push out the cone enough to make it easy to align. After looking into different possibilities this is the way I went.
I found this advice on another forum and I figured 9 volts couldn't really do any harm. I think you'd do more harm trying to shim the cone (in this case close to a 1/2") to be level with the basket.