There are plenty of bikes out there made with the wrong frame. Straight bars, columbias, hawthornes, chinese schwinns, even mountain bikes. The things you find on Google can be pretty hilarious. Most of the people on here use the correct frame, this is the Replica Prop Forum, after all. In the end, you should build whatever you want to build, out of whatever you want to build it with. Heck some people on here are making alternate universe versions, an evil X1, a blue one that Francis might have owned, etc. There's no wrong way.