Just for snits and giggles, I pulled out a couple of old manuals, and guess what, ALL the old loads are NOT hotter than today. Even some of the ones worked up in real guns, not pressure test guns.
Lyman 45th Edition (1970) does not have a rifle section for .357 Magnum. It lists max Unique with the 158gr jacketed as 8.0gr it also lists 8.0gr as max for the 158gr lead bullet.
The Speer #11 (1991edition) in the RIFLE section using a Marlin 1894 as test gun, lists Unique and the 158gr jacketed with 8.2gr as max, and 6.0gr as max with the 158gr lead bullet. It also lists these exact figures as max in the pistol section, using a Ruger Security Six as the test gun.
DO note how these loads are well below the 8.8gr loaded by the OP.
Unique is not the optimum powder for max performance in the .357 Mag, it does gain some benefit from the carbine length barrel, but not as much, proportionately as the slower AA#9, H110, or 2400.
Unique will get a 158 into the 1450fps range from a carbine. 2400 will get you into the 1800fps range.
Bullet selection is most important, anything made to expand well at pistol speeds has a good chance of overexpanding and under penetrating at carbine speeds.
A couple of points about the Marlin carbine, I've had a few of them, and sometimes they are not happy with feeding SWC slugs, and they are never happy with rounds that are too long. Other than that, they are light, handy, efficient little guns capable of taking larger game than many think, with the right load, and proper shot placement.