What about this?
http://www.musketvtwin.com/home.html
A guy has built a rather tasty bottom end which accepts Royal Enfield jugs and slots into the standard frame (with slight stretching)
I remember seeing this after he scratch built his first one. From memory, he's an Indian guy, and did it in his spare time in his shed over 2-3 years. I did think the barrel's were a bit far apart, but much improved to my eye since he's tightened them together.
Since we're talking specials. Here is the Indian/BSA special that I built. It's a 500cc engine (bored out to 580cc). Loads of torque and will knock spots of my 600cc M20.
I went to the Wednesday bike meet last week and saw this. Not a bad replacement for a 16H engine Sorry I couldn't get a very good picture as the sun was so low and bright.
That's a tight squeeze and really fills the frame. It looks great. Is that an actual Matchless engine? The Brough boys must be spluttering into there pink gin's. Ron
The original front down tube has been cut away and replaced with an "S" shaped tube to clear the exhaust. The 16H frame and forks were quite rough and pitted, it looks like he's rescued it from the scrap heap. He's managed to make a silk purse out of a pig's ear