ORIGINAL: FA
I think the 336 youth model is no longer in Marlins lineup, but the 336 is short rifle anyway. The 336A doesn't come with a thick recoil pad just a plastic cover so it's a little thinner.
Why not just cut the buttstock down to the LOP you need and install recoil pad? I did that on a Marlin 1894 357mag. for my son. Itis the one that has the birch stock. No way I was cutting down my own 1894c with walnut stock.