I have UBB classic 6.7.1 and it still works like a champ, but there's no way to stop the spam registration I have to weed through every single day. There's no way apparently to install a CAPTCHA program on it. So now I'm thinking of updating to Threads, but I'd like to keep as much of the old 'look' as possible. Does Threads have to have those right and left margin boxes?

Yes, you turn the left & right columns

Below are some of the settings available to you...

Only show left column on portal page?
Only show right column on portal page?

Allow users to turn off the left column?
Allow users to turn off the right column?

The styling system also has a LOT more options...

No you don't have to show the columns if you don't want to.

As for overall look and theming, that is slated for an upcoming upgrade which I hope comes soon. No actual set time but it should be in the works soon.

You can do color and image theming but very time consuming and an all new method should come soon that hopefully will be much easier for the average user.

There are other options as well if you'd need board customizations or styling... Several of us (me for one) do a lot of 3rd party styling (heck, I've been known to sell a style or 20)

I'm interested in having my islands showing on the bottom instead of on the right or left. Is there a way to easily change this?

There is a post at UBBDev (templates forum) where I discuss moving the WoL to the bottom; the same can be adapted for any CI