First off unless they are aftermarket springs your buddy has. They will not give you 3'' of lift.
Stock Rubi springs only have a higher spring rate than normal TJ springs.
They are the same height. Just stiffer. Most ppl that install Rubi springs claim to get lift from them.....truth is most that swap them out have sagging springs. So they don't really give you lift just gets you back to factory height. They mite,, just mite set you maybe 1'' taller then your jeep came stock.
If you have saggy springs....Yeah swap them out, the rubi's spring will do you some good.
As for the shocks....that's up to you, if your shocks are old or leaking...Yeah swap them out too.
Any more question's let us know..
again rubi springs are NOT 3'' taller than normal TJ springs.