How much work is the tunnel replacement? I have not build the Goblin myself and it seems like the tunnel is a core part of the chassis.
Including painting the new parts, you could probably do it in a weekend.
The rivets take a few seconds apiece to drill out, they are aluminum and very soft. The bigger issue is removing the old tunnel cap, which is very long, and unwieldy to thread out of the now built goblin. I honestly don't remember how I got it out, but it's a real chore. It's captured in between the firewall in the rear, and the bulkhead in the front, and since it's all one piece it's just a real struggle to get enough room to remove it. You'll have to remove the seats at least.
The new tunnel cap is a three-piece design which goes in really easy. I had to drill new holes for the rivets to go in, it did not reuse the existing holes. Rivet the three new pieces in place, install the shifter, and you're done.
It's a worthy upgrade in my opinion. I had the group buy billet shifter previously. Although it was very beautiful, the shift action left a lot to be desired in my opinion. The new DF shifter fixes every issue I had. It doesn't have quite as much bling, but if you want to drive your car more than look at it, it's the shifter for you.