The M951 is one of the more easily modifiable lights, just open the head, remove the lamp assembly and place in the new LED module. Like the other posters have mentioned the Malkoff M60 or M60W are pretty highly regarded and are pretty tough (they have been tested on rifles) and if there are any issues you can contact Gene and he'll fix it.
If you do decide to get a M60, don't forget one of these fitting rings, as you need one since the M951 has a shock absorbing head. Without it, your module may not light or have intermittent contact issues.
http://www.malkoffdevices.com/shop/...zel-p-6.html?zenid=kdjicnpfceimidcpa9s984mb61
On the other hand, you can look up Nailbender in the Custom Mod B/S/T forum. He can build a variety of drop ins for different purposes. If you have any questions feel free to post or PM him, he's very helpful.
Take a look at Post #1 to get started:
https://www.candlepowerforums.com/threads/248771
BTW if you do decide to purchase a module from Nailbender, they come with a spring and you would need to install that spring on the bottom of the drop in before screwing the head down. Both of my lights with a Z32 and M2 head both required springs for the modules before they lit up.
Happy Hunting!