Reg - You can't see a gap because from the angle the picture was taken, the "cut line" is under the aft lower frame (stile) of the galley cabinet (the one that runs port and starboard across the new sole). Once I had a template I liked (several versions were used, as I changed my mind on some things), I cut the forward-most 7.5" off the forward end of the sole, then epoxied and finished each piece separately. That put the cut under that cabinet stile. The Admiral and I debated quite a while on where to put that cut.
My comment about not running the sole under the "vertical piece" of the cabinet refers to the panel on the midship end of the galley cabinet. In other words, I chose NOT to extend the sole in the midship direction all the way to the teak grating that sits under the companionway stairs. I hope I said that well. Maybe this will help. If you go back to the original post and look at the bottom of the 3rd picture, you will see that the teak grating bumps up against the galley cabinet. That is the "proper" location of that grating - it has been slid as far to starboard as it can go. Now look at the bottom of the 4th picture. The grating is missing, but you can see I could have made the sole about 1.5" wider, so it would have come out to that grating. I elected not to do that, for a variety of reasons, one of which is discussed below.
Important note: That piece of cabinet frame (I think it is called a stile) that hides my cut has a piece of teak plywood cleated to it, running port and starboard, and that ply drops down to the sole. If you uninstall it (it's just one cleat on the interior of the cabinet at the back of the stile, with 2 or 3 screws), you will have a MUCH easier time of things. If you want to run the galley sole all the way out to the teak grating that is at the bottom of the companionway steps, you can remove another cleat on the interior of the galley cabinet at the bottom of that midship panel discussed earlier. That cleat has two screws into the panel, and 2 or three into the sole. Once those two obstacles are removed, a piece of 3/4" ply will then slide fully under the cabinet. However, for reasons of geometry, you can only get the sole in if you take my approach and make it two pieces. Of course, reinstalling that second cleat will mean fasteners through your sole, and I didn't want that.
If you are set on a one piece galley sole, you will have to do what HMT2 did: partly disassemble the galley cabinet by removing the aft panel and the side panel (amidship) to which it is connected. Then the sole will (mainly) just drop in from above (after angling the aft end under the OTHER galley cabinet, under the sink). I didn't want to go through all that, so I struck what I thought was a reasonable compromise.
Sorry I can't help you with the idea of how well the new T&H ply will match the old, I'm working with plain fir. However, from what I've read, I would think that the way they are topcoated will make some difference, so even if they don't match at first, when the older sections need refinishing, you could switch to whatever varnish and gloss level you put on the new ones. Maybe someone else will weigh in on that.
Edited: If you read this before 0900 EDT on the day it was posted, significant content has been added.