I am sure that you will like it. The Remington 210gr JSP is pretty stout for the first time, but it brings a smile to my face every time
You will find more 41 mag online than likely anywhere else. I reload, so I have a replenish-able supply at hand.
My favorite powder is sr4756, but I am told that it was discontinued. If you check in over at the unofficial 58 club, several members have posted some of their own recipes for the 41 mag.
That 657 you have is a real looker! Please go out and dirty it up some so that mine won't be ashamed to show themselves in public