I have long arms and a long neck, so a 13 1/2" length of pull is too short for me also. Except when I am bundled up in hunting clothes, then it's about right. I solved my problem with a Decelerator Slip On Pad. At first I didn't think I would be caught dead with one, but since getting them, they have grown on me. I really like it at the bench, because it really makes me stretch to get to the scope and prevents scope bite. Plus, a doubled up pad is nice with a heavy hitter like your 338. I have a small, medium, and large, and the cheapest way to get them is at Wallmart. They are Decelerator, but the blister pack says Winchester. When I put my hunting garb on I just slip it off and everything fits for that application. Won't cost you much to try it and would give some time to really search for your final solution.

Good Luck...Good Shooting...Jim :-)