Believe it or not, that trike with 57 Chevy style backend is a standand model for Boss Hoss. You can buy one straight off the showroom floor of one of their dealers just like it, without needing anything customized....
They also do Vette backends too. Here is a Vette trike on eBay.
http://cgi.ebay.com/ebaymotors/Motorcycles___FLORIDA-502-CORVETTE-TRIKE-THE-FINEST-TRIKE-AROUND_W0QQitemZ130243364079QQddnZMotorcyclesQQddiZ2283QQcmdZViewItem?hash=item130243364079&_trkparms=39%3A1%7C65%3A1&_trksid=p4506.c0.m245.l1308

I've always thought they were pretty cool looking