It really is not enough that overall shape of jbeam matches, SBR 4 has engine at rear and has structural rigidity to have engine at rear, for front engine some adjustment probably would be needed. IRL stiffness of body is often mentioned, that has to do how car behaves, to get good jbeam such aspects would need to be thought out and that is really difficult part of jbeam. It just is not the same...
Possibly they just use those 'luxury' car mods from these sketchy Russian mod websites just to attract views. And trust me, I see a lot of these in those BeamNG 'car crash' videos that repetitively litter BeamNG YouTube searches.
Yeah, I just downloaded some again to see if any improved but was sadly reminded how low effort, low poly parts, no interiors, squishy suspension, paper frames, and usually old or broken audio. Beamng has set the bar pretty high with their official cars, I appreciate them so much more after trying these counterfeits.
I will tell you this is the most accurate answer you will get Half of the mods are on modsgaming.ru modsgaming.us and worldofmods.com the other half are private and you can't get them. And then there is another part there are probably like 2 wip luxury car mods on the planet