Mine is a 4506-1 with the beefed up frame, which did away with the "step" in the frame above the trigger.
But it has the squared off trigger guard. So I guess it is an in-between version.
Great gun and I use +P rounds in it as my home defense gun.
“There’s a rattle in my glove box,
A Federal twelve-gauge slug.” – Adam Carroll in song Porter Wagoner