I just got off the phone with the folks over at Delta. After a few minutes of frustration because the units they produce do not have identifying information on them, a measurement of the diverter from my house was found. I was in the same boat wanting a direct replacement but not finding a diverter that had a 1 inch thread for installation. the part number for the direct replacement in my home was RP38450. If you go to Deltafaucets.com you can check out the direct replacements.
The diverter on my unit worked fine until the shower was being used. In my case once the plunger was pulled up the water was finding a crack in the plastic insert which attaches to the adapter and 1/2" copper. The water was escaping outside this plastic insert and entering my walls. After cutting 3 holes in my walls and ceiling, removing the diverter and holding the end with my thumb, I discovered with the diverter off there was not a leak. I changed the o-ring and reinstalled the diverter, water again leaked. I removed the diverter and tested with plugging the copper line with my thumb again and there was no leak. After much testing I found that the water was finding a crack in the insert when the pressure was raised after the plunger was pulled and spraying everywhere.
I love the garrantee that Delta has, but I am pretty sure if this diverter was not all plastic the problem would have never happened to begin with. Delta gave me a 50% discount on the replacement part with a promise to refund if I sent them photos of the faulty part and a page in from my home purchase papers with my name on them. Seemed odd to only want a photo and the copy of my purchase agreement but its not my company. I wish they would have just wanted me to send them the faulty part and call it a day.
Moral of my rant is that there are 1" thread replacements for bath spout/diverters. Delta has them hidden on their website but a few part numbers are RP38450 if the diverter is 7 and 5/8" long, pull top diverter. RP17453 for a 1" thread 5 and 1/2" diverter, push nozzle diverter. The 1" thread works because Delta adds an addapter. This adapter does not need to be removed from your copper pipe if you get a direct replacement, and the direct replacement will come with a new adapter incase you do remove it.
P.S. DO NOT try to unscrew the adapter from your copper pipe. Bad things will happen if you do!