What a wonderful gift!
It's easy to get or make low pressure loads for 12 ga guns, so that good advice will be easy to follow.
As you probably know, the LCS stock head isn't the strongest design. To help preserve your original buttstock without cracking or worse, I'd suggest you stay with moderately-recoiling loads. Recoil forces are generally proportional to muzzle velocity x shot weight. I wouldn't shoot anything much over 1220 fps and 1 1/4 ozs of shot, and that much only when really needed, were the gem mine. (Loads in that speed range also pattern better than hi velocity loads, all else equal.)
You also might want to get a real expert to look at the stock head, repair any cracks that may have started, and judiciously inlet a small bit more in important, invisible spots (like behind the back ends of the lockplates). Adding a little bedding 'glas carefully, in critical areas, will also greatly strengthen the stock head. An ounce of prevention and all that ...
Some people who do widely respected stock work of that nature include David Trevallion, Keith Kearcher, Buck Hamlin, Dr Bill Hambidge and I expect Doug Turnbull.