I've got a 2001 frontier standard cab. i lowered it 3 inches all around just using blocks in the back and loosening the torsion bars in the front.
you can lower the front, and it will take it slightly out of alignment, but it stays in the "green" region. meaning its still safe and all, however it would actually be better to get it realigned.
the only problem is youll probably need new shocks for the front, its a bit more bouncy due to the loosened torsion bars, mine doesnt do that anymore though. just dont
slam it using the torsion bars.
alltogether, it only cost me 30 bucks and about 2.5 hours in my neighborhood's parking lot with just me, the jack, two jackstands and a normal set of tools.
