The way I see it, real world doesn't follow a pattern, so it's ok to replace the vehicles with other vehicles not 100% resembling, as long as it's realistic and the vehicles has the same features (but many vehicles resembles the original vehicles. Notice not all vehicles has 100% correct resemblance, for example the Landstalker, Cognoscenti. It will also feature unique handling made by 'Killatomate85', maker of 'Realistic Driving & Flying', made after request for this pack.
Grand Theft Auto Ultimate Vehicle Pack will feature realism, quality, and variety. This is the download for my WIP vehicle pack that I started in August 2009, after seeing all the other packs containing only super cars.