The only way I know to be sure if it's a round or square butt is to remove the grips. Most grip sellers have photos to compare to be sure you get the right ones.
You might want to look at Altamont grips. I have a set of the Classic panel with medallions in Super Walnut on mine. They were only $48. I don't see the Super Walnut offered on their web sight now though. They have a new classic look that I think matches the new classic revolver.
You may want to do a search on here for the revolver check-out procedure. When you look at the gun, you want to check for things like hammer push off, end shake, etc.
Lots of conversion grip options out there but they will be either the combat or target style which are larger than the magna style you have pictured. Altamont and Ahrends are just a couple. I would check out the Classifieds forum here to see what you can find.
Be careful while shopping for rim fire snap caps. Many are labeled "not for dry fire...". Unlike center fire snap caps with a spring loaded center, most rim fire are solid with no way to absorb the shock.
The Model 19 is one of my favorites too. Here's a pic of mine. Not sure if the stocks are original and they are a little big for my hands but I love the way they look.