First off the Marlin 336 is a classic deer rifle and the 30-30 is a classic chambering. With just regular remington core lokts he has the capability to kill a deer cleanly up to 200yds. This is with either the 150 or 170 gr loading. Some 336 rifles prefer one or the other. Bolt action rifles in high intensity cartridges are nice and definitely have their place, but the average shooter has no business shooting past 200 yds in the first place. I personally don't do it and have been shooting and hunting for years. Its just a personal thing for me. If a man has the money and can buy a new rifle to hunt with then more power to them, if they don't and have to stick with a 336 in 30-30 then don't think for a second they are not sufficiently armed. Don't let the gun mags persuade you or your buddy that you have to have a 300 mag to hunt deer. It just ain't so. As far as the leverevelution rounds go, I don't have a lot of personal experience with them. From what I do have they do extend the range of your rifle some. In most conditions it is irrelevant. It may give you an extra 50 yds or so, but the shooter has to be capable of making the shot. No ammo is going to make up for shooting ability. I have also heard some that have been dissapointed with their performance at shorter ranges.
Basically, if I was your buddy, I would hunt with that 336 with either 150 or 170 gr core lokts, keep my shots 200 yds and under and be happy. Hell 200 yds is a long way.
Mike