I tried steam workshop downloader but it didnt work.

I would like to know that too. Postal 2 without AWP forever, AVPC, and some other workshop mods is quite barebones.

you know that the latest gog version of Postal 2 does by default come with A Week in Paradise correct?

lol

and clearly if you want mods for the gog version of the game youll need to use the Complete original version from Extras in downloads.

as the offline backup installer version does NOT support steam mods or old mods from what I remember plus it doesnt support MP like the steam version does as well

The AWP that is included in the new version is a shadow of its former self, namely missing levels, minigames, missions and whole weapon packs that the original AWP already had.

I'll tinker with the complete original version as per your instructions, thanks!

Actually it is just a game mode called A Week in Paradise and not the mod with the same name. Postal 2 on Steam (but I guess this is the same on GOG as well) comes with the base game and the expansion bound together and while playable separatelly it work simply by loading Apocalypse Weekend right after you finish the last day in the base game and that is all. The effects were updated as well to improve the quality.

The physical boundle called Fudge Pack however comes with the mod A Week in Paradise. All weapons and features from Apocalypse Weekend appear in the base game. Weapons like the katana was also added to all days and can be found somewhere.

Paradise Lost is not compatible with Fudge Pack but Eternal Damnation is included by default there which however had problems with the Steam version.

Personally I kept the Steam version but not really played it after completed Paradise Lost. Whenever I had the urge to play I always installed the Fudge Pack for that reason and it works better with mods including the coops.

There are certain mods that have GOG support. AWP Forever is one such mod. It adds in the lost content from a Week in Paradise and it should be compatible with Postal 2's latest update. Another mod that I know is compatible with the GOG version is 5024x Patch (aka X Patch). It adds bugfixes, rebalanced weapons and more. Its in beta at the moment. Also, there is an add-on for X Patch that adds better sound effects for weapons. Another thing to note is that X Patch will have 3 final versions.
One that will be only bugfixes and Paradise Lost weapons in vanilla Postal 2 (vanilla+).
One that will add improved gameplay (enhanced).
Last but not least, there will be an AWP version that combines A Week in Paradise Forever, the mod I talked about earlier, and X Patch itself.
I recommend you check them out if you are looking for a couple of mods that are compatible with the GOG version. I used them before and I had a good time.