I looked at those, but they were different. Checkering on ones I have is not as large an area as those. Also checkering on back of ones I have is only on back of left side grip. Ones shown in link has checkering on back of both panels. I'm thinking maybe Buck Rogers ray gun grips, ha. They are large and odd looking, but surprising they feel really good on the 25-2, 6.5 bbl, they came with.I think that they are these: Target Revolver Gun Stock
You know, I didn't even notice the slight suggestion of finger grooves until you mentioned it. Only markings on inside is "45". They really fit the 25-2 well and it's probably a '70 to '72 made revolver. They are fitted to top of backstrap, underneath and side of trigger guard and to side plate perfectly.I'm away from home, so can't check my picture file, but as I recall the slight suggestion of finger grooves is a Mershon identifier.
Here's a 1962 ad with a not very good picture.
Linde reminded me that he has a pair of grips like this that are marked as made in Italy.
To add to the mystery, note these two seemingly identical boxes, one printed Sile and the second with a Mershon label pasted where Sile would be.