Steer clear of cheaper imported springs - (Belton etc) they just aren't the same quality and will cost you more in the long run. A decent smithy (bayside springs etc) can repack yours to whatever height/rates you want and a lot cheaper than new gear.

For a '75 I'd definitely recommend greasable shackles front and rear for some comfort - they do make a comfortable difference, as do airbags.

Springs are easy enough to do as the others have said if you have some gear - jacks, stands etc.
It can be a dangerous exercise without the correct gear though, and you don't save that much money for the risk involved.

C.J.