Congratulations on your new used rifle dude. You will be happy with your Marlin. I own 3 of them, a 35 Rem, 45-70 and 44 mag. Well made rifles that will last for years with proper care and you can pass down to your son or daughter. Glad to see you opted for the 30-30 over the 357 too. A much better choice.
This wouldn't be my first choice of rifles from my safe for mulies but if you stoke it up with 170 gr FP ammo and keep your shots inside 150 yds you should have no problems. Just take your time and put the slug into the boiler room. Good Luck getting your tag.