Basically, any rifle that you would take a heart/lung shot on a deer with, you can do the same on a hog. I have killed hogs with shoulder shots with calibers ranging from 243 to 300 WSM. Any caliber in the 270/308/30-06 range would be more than enough in my opinion. As I said before, since you already have a Marlin 336 in 35 Rem, that would be my choice, and coupled with Hornady LeverEvolution ammo, the 35 Rem is going to be hard to beat for close to medium range hunting. My son and I have had absolutely no trouble killing hogs with our Marlin 30-30's and LeverEvolution ammo.