The Univeral Carbine that you have is one of the "imporved" types. It is similar to the GI models in looks, caliber and operation. I have had several of the ones that are kinda G.I. Those were made or sold by Iver Johnson, Plainfield Machine, Universal, and IMI. Those have alot of the GI parts in them or are up to specs. However, most had aluminum lower receivers with some GI parts. The rest of the guns were pretty much the same as a few actual GI guns that I had.
The so called improved Universal had 2 recoil springs under the barrel, where the GI guns only had one. The operating rod/slide/bolt carrier assembly was hardened stamped, while GI guns were machined steel. Sights are somewhat different, as you have found out. I remember them having a "flip" type of manuql bolt hold upen on the receiver, where the GI guns just had a small push button on the slide./bolt carrier assembly. IIRC, they all used the same mags. Some had the "flip" switch safety, and some had push botton safeties. Can't remember which had which.
And the stories you hear about the operation of the guns is also common. I remember having 2 different ones. One worked perfectly well and the other had feeding problems. Neverfigured out why. Switched mags etc. Maybe spotty quality control. Tje early guns made by Universal were more true to GI form. The later ones were the improved ones.