Hey 49er, Just finished my '48 and it to had 1/4" on the rear and 3/16" up front. Went to my auto parts(NAPA) store and bought 1/4 to 3/16 threaded adpters. They worked just fine. I also found out that if you cannot go 1/4" , the 3/16" will work just as good. You will find that out if ever you decide to install disk on the front. Another story.
Good luck, Mike