A stand in for fitting lids

I have the roof/lid floating panels assembled for the reliquaries, but then am faced with cutting them to size... a thing complicated by the angles. They have to be cut at a 70 degree angle along one edge and to fit the top rail at the other.

Since it is impossible to put an assembled lid in place and mark it for cutting to size, I use a stand in. By fitting a narrower piece, I then know the angles and table saw settings to cut the lids, taking those settings from the perfectly fitting piece as shown in the photo.

Make, fix and Create. Give your life greater meaning.