These are the primary tools used to carve the top. The same finger plane that was used for the outside is used, in addition to a thickness caliper to measure thickness. I carve the top to the desired arch and use the caliper to measure how much to remove from the inside.

Laying the plate on top of the sides form holds the top steady allowing you to carve without marking up the outside of the top.
Here is yours truly hard at work with the finger plane.  This top is german spruce, and is a pleasure to carve.
This picture shows the holes I drilled with a forester bit to gauge the depth to carve. I set up a forstner bit on my drill press, and set it up to where it would drill down to a few millimeters less than I'd actually carve. This is just a simple way of knowing when you're close enough to start worrying with the calipers. On mandolins, I use the forstner bit to remove as much excess wood as possible, but I have a small drill press, and that doesn't allow me to do the same with a guitar.
Here's a shot of the top after a couple of hours work with the plane. At this point, the top is a uniform thickness, but about 3 millimeters thicker than the final product.

I have a Merlin carving machine on order, which I'll use to make a copy of this hand carved top to use as a template for future guitars.

With the top now at the right thickness, all that's left is to smooth up everything with my Orbital Sander. Here's another good example of buying good tools. I had no idea how much use this sander would get when I purchased it.