I got home this morning at 0545 after flying 3,350+ miles yesterday, so a nap was in order. After sufficient sleep and pro-caffeination, I made my way out to the Garaggio. There were a few details to work through on the firewall template including drilling 6 remaining mounting holes, mounting the ANL current limiter for the alternator, and finishing the lower right corner of the firewall perimeter.
Once that was all done, it was time to start working with the stainless steel sheet metal. So I traced everything out. The perimeter is very accurate by going to the inside of the sharpie line. You may also notice that there is an odd shape along the middle sides of the firewall. I will address this tomorrow. The marked holes will not be 100 percent accurate when transferring their location this way. I wish I would have thought about this ahead of time, though I have a plan. I am going to drill them under sized. I will then verify the pilot hole is centered in the existing hole in the firewall and step drill until I hit an edge of the existing firewall hole. Then I will have to get the needle files out and enlarge the holes using the plywood firewall as as my template.
If I would have thought ahead, I could have avoided this. What I should have done was made the firewall template before I mounted accessories on the firewall. This would have allowed me to match drill everything in place. Set the stainless firewall in place and drill it once. I would have ended up with perfectly matching pieces. Seems obvious now. But I didn’t so its a bit of extra work now.
Hand shears were the tool of the day. The stainless is very thin, so it is relatively easy to cut by hand. I am actually able to get a nicer cut on the stainless than I did on the aluminum baffles. The aluminum deforms easier and when shearing if you are not careful the sheet metal becomes wavy. No such problem with the stainless.
Next is to cut out the areas around the engine mount extrusions (the ‘L’ shaped marks), the aileron torque tube bearing, and the studs on the firewall. This will allow me to put the firewall into its final place and check the perimeter. Cutting out the L-shaped areas and the rudder cable slots is tedious. It is a mixture of drilling holes, using the Dremel, and hand filing. I am admittedly going slow to try to make the shapes as accurate as possible, but it is taking a significant amount of time. Even so, I am hoping to have this piece of the firewall done tomorrow.
the Garaggio 
You may have already done this -but to avoid wavy cut edges in sheet metal when using shears/snips, just make a preliminary cut about 1/4″ or so from the line and then come back and trim again to the line -the thin strip curls away and leaves the larger piece flat.
Thanks for the tip! Works well!