Let me preface this post with the statement that I'm not mechanically savvy and have limited information on the question about to be posted.

30 years ago my church purchased an Econoline van for a missionary in South Africa. Since then he's refitted the transmission with one from a Mustang. The speedometer gear no longer runs in the positive direction (goes toward zero). He has an 18 tooth, yellow nylon speedometer gear he'd like to replace with an 18 tooth, yellow nylow Left handed gear. Any such item exist? Is there a work-around solution?