You’re on the right track. The part of me that goes to shit quickest is my feet from uneven terrain. You can’t duplicate that in a gym IMO. Hiking in real off trail conditions helps. Walking back and forth side hilling with a weighted pack and your mountain boots on a steep hill will help prep your feet and ankles.
Don't forget about the mental aspect of the hunt. I believe that a good attitude trumps being in good condition. I've seen guys in far superior shape that myself (not that hard to do) that really struggled on different hunts. There are times you are going to feel like complete crap. Don't forget to drink, eat and sleep. Sounds silly but you can go south fast when you are burning tons of calories and not replacing them. If you can manage a few trips with your pack and gear that would be great. Even if it was car camping and taking a good long hike during the day. Your ankles, feet, legs really need some time in the outdoors with a loaded pack. Maybe not 60#'s but a solid 40-45# will help you a ton when you hit the field.
Bring a bow or a gun. Not both.
Embrace the SUCK and Remember to have a good time and soak it all in.
I'm 60. Started sheep hunting at 43 I think. Made it into the sheep mtns 13 of those years since. Headed out again this year. In addition to an active lifestyle my sheep sheep core exercises are squats, rigourous cycling and hiking UP AND DOWN with a pack. Slowiy working up in weight. Nothing compares to hiking up and down with a weighted pack. If you can't find hills or stairs try doing step ups and down off a solid box. Or at least hold on to your counter top and do one legged squats. You need to be able to lift your weight/pack weight over and over again with one leg. Thats what we doing in the mtns. Doing wall sits can help condition your quads for going downhill with a heavy pack.
I think only one other guy here mentioned Squats. They make you strong all over. Do them right and make em count. They should be a core part of your routine. Once a week followed by an adequate rest day or tow depending on how fast you recover. Don't overtrain! We ain't no spring chickens no more!
Down the road, in a gym far away
A young man was heard to say,
"No matter what I do, my legs won't grow!"
He tried leg extensions, leg curls, leg presses too.
Trying to cheat, these sissy workouts he'd do!
From the corner of the gym where the big guys train,
Through a cloud of chalk and the midst of pain,
Where the big iron rides high, and threatin' lives,
Where the noise is made with big forty-fives,
A deep voice bellowed as he wrapped his knees,
A very big man with legs like trees,
Laughing as he snatched another plate from the stack,
Chalked his hands and monstrous back,
Said, "Boy, stop lying and don't say you've forgotten!
Trouble with you is you ain't been SQUATIN'!!"
Lunges, jump lunges, back squats, jump squats. Don’t look past the need for muscular strength and muscular endurance. Intervals on a stair climber (Jason Hairston did a 16 min workout that I use, and seems to help more than a flat walk with a pack).
don’t hurt yourself training, and don’t overthink it.