Concerning modern H&R barrels, only the Buffalo Classics( and some rimfires) have dovetailed front sights, all the rest are screw mounted, see the Peep and Firesights link in the FAQs for suggestions on screw mounted fiber optic front sights. If your 357 has a Williams WGOS barrel sight, you can order a fiber optic ramp for it, they'll be able to tell you what front sight to use also, their number and sight height calculators can be found in the peep/firesights link.
Tim