Seriously, though, I've have an old British motorcycle for a long time, and over the years I've made changes for convenience and comfort, like adding turn signals (safety) and raising the handlebars. It was a "cafe racer" and with the short handlebars it was like riding a jackhammer.
As is, I can probably get around $6,000 - $7,000 for it; but the other day I was told that it would be worth in excess of $30,000 in original condition! However, the box where I kept the original parts has long since been lost or thrown away.
BSA, Triumph, Norton?
Have you checked the online Brit bike shops that are here in the U.S.A.?
Just ride the bike and enjoy it, and hunt for the missing parts as time and money permits.