Thanks for the images!
I am pretty sure this particular bike was a one off job. Phil Vincent had a deal with the Chairman of Indian to provide engines for Indian. It was done on a handshake and prior to the deal being inked the Chairman was replaced by the Board of Directors. Vincent was relegated to using Indian as a distributor only.
There were several prototypes made, but only one of the conventional Vincents as seen here. There were two, I believe, of the Vincent engines in the Chief frames.
The bike pictured here was given to Phil Irving and resides in Australia. The current owner has done a detailed history of the bike, which was published in bike magazines in Australia. For some reason these bikes were not of interest to me, so I only followed the subject in the most general way by keeping an eye peeled.
To John Romano,
You finally move to my neck of the woods after I moved out! Good to hear from you.