Once you have the correct body installed fire it with the sight all the way down. If it shoots high you need a shorter sight blade. If it shoots low run the sight up 4 full turns, If it is still low you need a higher rear sight blade.
When you install a new blade DON'T stake the windage screw until you check out how it shoots to elevation. Once staked the windage screw is hard to save for reuse and adds to the cost, at Midway a blade is $5-6+ and a blade and screw is $13.20. At Numerich the blades or screws are $13+ each
The .146 height sight blade is about the middle of the road. .086 is the lowest for K,L,N frames and .190 the tallest
Here is a chart that says a 6" model 48 takes a .146 rear blade. Click on it to enlarge