Ok just found a gtr frame I'm gonna swap my motor over to. When I built my boat I had I built with the idea in mind that I might put a gtr on it some day. Fast forward motor I put on it isn't working out and the gtr is coming. Transom was built cut down in the middle and will be built up the the specified 21" for the tall transom. My question is this, do y'all think a 17* transom will hurt any vs the recommended 20*? I wanted the transom built to gtr specs just cut down a little, but somewhere along the way it got built to 17* and not 20*. Most people have said they wouldn't worry about it and that it most likely won't effect anything. Just want to get some more opinions.

Shim it

What does shimming consist of? Is that just something I have the builder do when he raises the transom height?

You definitely want to shim it.

Anything less than 20 deg. and you drastically lose performance.

Couldn't you just change the pin hole for a quicker fix?