The Zamak 5 formulation that Henry uses in their RIMFIRES has such a minor "shrink percentage" that you'll never notice it & neither will your kids. It's a very stable material.
It won't affect function, it won't even be detectable without some very precise measurement capabilities.
Just not an issue.
As far as not holding a candle to a 39 goes, I have a 39 variant that's somewhere between 12 & 15 years old.
I also have the Henry Golden Boy that I personally ran 28,000 rounds through in three months last Fall.
The Henry busted one locking bar spring well into the test, easily replaced, and still functioned even with the spring in three pieces through several thousand more rounds to finish up.
I replaced the extractor late, but I'm not entirely sure it needed it.
The Henry was far slicker out of the box than the Marlin is now, after I don't know how many rounds I've run through the Marlin over the years.
The Henry was more accurate new than the Marlin, and I haven't fired the Marlin for accuracy in recent years, but I'd suspect the Henry still is more accurate.
Fit & finish are better on the Henry.
I also have my Grandpa's Marlin pre-39 .22 levergun, dating from 1910-ish.
My earliest memory of that gun as a kid was when it would have been roughly 50 years old, and it had a busted bolt (front inch cracked completely through) at the time.
The idea that a Henry .22 levergun can't hold a candle to a marlin 39 doesn't jibe with my experiences.
Just as accurate, if not more so.
More than durable enough for a lifetime of shooting.
And a quality rifle despite the alternative construction that bugs so many people.
Track down a copy of the 28,000 GB run in the current Guns Of The Old West Magazine.
The thing wasn't even cleaned till it got to 22,000 rounds & it was still running.
Try that with a Marlin & after 28,000 rounds through one, tell me again the Henry can't hold a candle to it.
As far as the finish on the "black" rimfire lever models goes, Henry offers a range of pricing & features that Marlin never has & never will.
The black receiver covers are used on the entry to mid-level models.
You get up into the higher-end Golden Boy & I'll tell you that brassy receiver cover coating is hellaciously tough.
Even using a glove through most of the endurance run, it shows no signs whatever of wearing off.
Denis