" But, they're no longer made, and they can be stupid expensive."
My M-60 came from the factory with UM's combat grip, and as far as I'm concerned they're deschiznit. I've tried others for improved concealability, but they've all been short-lived experiments. UM's boot grip, real S&W wood grips with medallions, Barami Hip-Grip...I liked the Barami the best by far, but .357s were nowhere near as comfy as with UM's combat grip.
Time = money
Buy the UM's once and you'll be set free.
Your J will be as easy to hold as a 1911.
And if you want to sell them in the future, unload them on ebay.