Unreal is another one of those classic games that includes various hud options out of the box. Depending on which version you have, normal or gold, the menu will be different, but the outcome the same.
However, to disable the crosshair, open the Unreal\System\User.ini file.
At the bottom, make sure the following section reads as such:
There is no Crosshair=8 option, so when you set that, it loads nothing, getting rid of the crosshair. This option may reset if you edit any settings in game, requiring you to re-edit the User.ini file. The option to disable the gun model is built into the game menus if you want to do that.
This screenshot is taken with the unofficial 227h patch and high resolution textures.