Welcome! The model 158 was made by H&R Inc who went out of business in 1986, that's why H&R1871 doesn't have information on it. All H&R Inc firearms had cast iron frames, 44mag was one of the chamberings that were offered by them, so you're just fine, H&R1871 offers the 44mag on SB1 frames which are also cast iron, so you're good to go.
If you spend some time in the FAQs and Help sticky as Kurt suggested, you'll see that your AY frame was made in 1982.
Tim