Hi there,
Unfortunately I am honestly not fully sure but if I had to hazard a semi educated Guess I would probably say no, I could quite easily be wrong but both versions of the game's code does differ slightly that's why its a pain to get US Codes working over here.
If it's any consolation to you, I tried a few different conversions for your Full Garage code that WILL NOT! work over here so I am currently buying every single car manually lol for upcoming updates to the save pack.
I don't know if you or anyone that reads this could do something like this but; get PCSX2, use an EU BIOS and get an EU iso of GT4, find the codes for the cars in the PAL game, using something like HXD Which is my personal preference for hex editing and if anyone with knowledge of how to convert hex code to cheat device code for the PAL game, then I will be more than happy to convert that to a US code for you to try. 
Might be a long shot but could be worth it.
Last edited: Mar 14, 2017