I dunno if the modern steel frame Henry is lighter than the original iron or not. Steel is stronger than brass but with the pressures involved it won't make any difference. The toggles in the action will give out before the frame does.
Whitneys were all .36, no iron frame S&B's, no iron frame G&G's. Schneider & Glassick made a 51 copy in brass but there's only three known and one of them is iron. No brass Remington copies.