Joined: Feb 2012
Posts: 19,373
Likes: 5,515
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Why does the joint require a plate? A piece of tubing might serve well here. I'm also curious to why you're using a twin tube top tube.
I also see that your design shows a segmented fork. Do your homework well with it. Search this and other building forums for others' experiences. Andy.