I made the Marines of OP4 maintain this essence of the Marines of Half Life and earlier. As if they came out in 1997/1998.
Well, maybe you've ever wondered why OP4's marines are so different and detailed from Half Life (Aside from being models made to be NPCs instead of enemies, and by another company...) It's because Half life models 1 were practically ported from their Beta, and those of the beta successively, from the alpha, and they were one of the few NPCs in the game that did not experience major changes beyond the texture.
Now, after this unnecessary story: I have made the Marines of OP4 maintain this essence of the Marines of Half Life and earlier. As if they came out in 1997/1998.
And unlike my previous addon, which is more of an appearance change to make them similar to their original version. This addon is a total rebuild of the models. The one where I did my best to make them look like HL's vanilla Grunts
Beyond that, there are not many more to explain that cannot be seen.
To Davidoon and his incredible addon "BetaPack900 For Half-Life" from whoever took the head of the engineer, and I also base a lot on his work. Its addon can be found in MODDB.