What ratchet shifter are you using with a 518 46RE ?

The 518 is not a 4 speed. It is a torqueflite 3 speed....same basic innards as any other 727 torqueflite.......with an ELECTRICALLY controlled OD hanging off the rear

The shifter "should" be same as any other TF unless they made the shaft different. You will however need whatever shift lever supplied with the shifter

EDIT......I did not mean to imply the trans is not electronic. If you truly have a 46RE and not an RH, then you will have a multi pin (more than 3 pin) connector pointing "vertical" to the rear of the shift shaft