throw the "maps" and "models" into: 
Mafia > Mafia

This is a mod created by me which makes Vito and Joe the main characters!

What the mod does:
Replaces Sam With Old Tommy (For it to fit with Joe and Vito)
Replaces Tommy with Vito
Replaces Paulie with Joe
Replaces Joe with Paulie
Replaces Vito with Sam
Creates custom HUD Icons for Tommy, Paulie, Sam and Salieri replacing them with Vito, Joe, Old Tommy and Derek.

Bugs:
Joe's Mouth wont move, i can't fix this
Old Tommy's death model has only one facial expression, same issue with Joe, mouth wont move.

Files you need to download:
Derek Pappalardo Mafia 1 Mod - https://www.nexusmods.com/mafia/mods/51
Steve Coyne Mafia 1 Mod - https://www.nexusmods.com/mafia/mods/52

In the models folder in the mod, i replaced the low quality models of Frank and Salieri with the high quality ones. So just install the maps files from Derek & Steve mod to have them high quality in-gameplay.

Credits: Meta