If you need help or advice fitting it, ask me and/or Pettifogger (I'm offering his advice without consulting him, however)... A new or spare part arbor will probably not be friendly enough to screw in and clock up to wedge alignment, and may need either a shim or a shoulder cut to get the wedge slot aligned. Make sure the protruding threaded portion at the rear is trimmed to flush with the frame so it doesn't interfere with the hammer fired position.
At any rate, there are people on the net here that can help.
One advice is to thread the locking pin hole and use a #6 set screw instead of a solid pin to lock the arbor, this will ease any possible future removal or adjustment. If the arbor came out of another gun, hopefully the locking pin cut and the wedge slot will agree with each other, if not you may have to relocate the lock. Also make sure the arbor is right side up, as the wedge slot may be tapered to match the wedge.