GTA IV Ultimate edition not working anymore after installing LCPDFR 1.1

[ScreamingFrancis 28]

Ok, here's the problem: I have the Steam version of the game, with the Patch 8 on, so I had to downgrade both GTA IV and EFLC, but applying the downgrade screwed the game up: I simply couldn't start it anymore, no matter what I did. Didn't even try to install LCPDFR there.
I decided to leave Steam version alone and tried to download an unproper game version by Prophet, who had the Patch 7 version and tried to install LCPDFR on that, but the install asked me to "put the files in the same directory of my EFLC folder", which I did.
As a result, EFLC didn't work anymore and GTAIV didn't read the LCPDFR at all (Alt + P and stuff). I checked the Diagnostic tool and it said everything was ok, although the mod was installed in another folder.
Changing the installation folder to GTAIV root folder had the result of screwing the game up even more, giving errors and errors, and it's patch 7.

Again, I know that developers do not support unproper game users, but I had no other way to downgrade my GTA IV!

Am I missing something?
I need some help to fix the Steam version  downgrading somehow or the unproper version at least.

My specs: 
Windows 10 Home
1703
Intel(R) Core(TM) i7-4510U CPU@ 2.00Ghz
8,00 GB RAM
64bit System
 

Edited July 2, 2017 by ScreamingFrancis