I found nothing locally when adapting a standard remote mount 3/4" x 16 other than going to a machine shop. So ended up buying from the above same ebay supplier, nicely made.
On my true amsoil dual mount the 1" x 16 is not a 3/4" x 16 male adapted but a true 1" x 16 male threaded into the mount. My guess is their singles are the same.