i don't think autolite makes a side gapped plug but alot of people side gap the plugs themselves. click on link below and it will tell you some good information and show you the proper way to side gap a plug..... buy a set of 3924's and follow the instructions in link and let us know results thanks...
It's been awhile since I researched the factory backcut plugs. For Autolite, I think their backcut plugs are in the Autolite Racing series (plug numbers start with AR).
I would check their site or call their tech line for info (this was just my foggy recollection, but it might get you going in the right direction).
I would double check that AR part number to make sure it equates to what you desire (I had thought that the AR3924 was the back cut version of a 3924, which you said you didnt want). I would check with Autolite phone tech or go to their site to be sure (I once tried to nav their site and it is all interactive and shut down my browser since I am on dial-up).
I cant honestly remember if they make a side cut 20 series plug.