I emailed Henry to ask what twist rates they use for various calibers, mostly because I was wondering what they used in the lever actions but also what they will probably use in their new single shot. Here is the reply:
Thanks for the inquiry. The twist rates are as follows:

.357/.44/.45: 1/38

.30-30: 1/12

.223: 1/12

I'm not convinced the twists on the .357 and .45 are correct, I've never heard of anybody using that slow of a twist for those. But I do see that they use the same 1 in 38 that Marlin uses for the .44 Magnum.

Gunnery, gunnery, gunnery.
Hit the target, all else is twaddle!