What power levels are you looking for? Something you can shoot all day in your Model 60, or some sort of full house loads?
The reason I ask is that it will make a difference in what powder you use.
Unless you need the higher-energy rounds, my choice would be a load equal to about 38+P levels. You can do this in either 38 or 357 cases.
I have always liked to use 357 cases in guns chambered in 357 rather then use 38's. Avoids having to clean out that crud ring.
All that being said, I have used Unique and W231/HP-38 for these types of loads.