Actually the TA22 Diff is Narrower. Either will bolt into the other. Mounting points are the same. The RA23 Diff is marginally wider tho. I had the measurements here somewhere.
Best bet is to take a trip to your local wreckers are measure two stock ones. My TA22 Diff uses T-18 drums so its a tad narrower again (2 or 3mm a side)