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Just to let everyone know I was able to install tAPI R11 and R12. When you go into the installer it will attempt to have you install tAPI under "program files (x86)" just browse for a new location and under your C: click the "GOG Games" . It will auto input Terraria so make sure you don't click on the Terraria folder inside the GOG Games folder. I did that the first time and it didn't work. C:\GOG Games\Terraria is what should be on your install destination.

It asked me if I wanted to combine this program into my Terraria folder and I said yes, made a desktop icon and it loaded up just fine.

I was never able to get some of the other mods to work like Game Launcher as it requires steam. This looks like it will be a good way to go. I loaded up world and was playing for about 2 minutes just to see if it worked. I will update if I find out more but I wanted to share this.

Thanks and please update with more info if you have any.
Game Launcher now works with the GOG version. Thanks for the update on tAPI...