In reality... a 1975 most likely has "settled" onto it's springs. That's pretty common in coil springs. You can buy new springs - not real expensive - I'd guess $300 - each end. Installing them isn't an easy job if you don't have special tool - and having it done will run you a couple hundred. Also have the front end aligned after putting in different springs. Or - better yet. If you car needs front end work... like new Ball joints, have new springs installed while they are doing the front end work. They will have some of the parts disassembled at that time. With replacing front springs your front suspension has to be taken apart. Rear springs are simple if they are coil. If they are leaf sring in the rear it's a little more work but still not a "big" job. Talk to some people at a shop that does front end alignments. They deal with this stuff every day. If the car drives and rides Ok - consider it a free "lower ride look" for free. Remember the saying "Praise the Low'rd"

Add air to the tires....seriously what part of the body do you think has "settled" ... look at it this way... many people work really hard to "cop" the top or "section" the body to get their body height "low"... your's might be natural.