Can I combine a Daystar lift with my rustys suspension lift? I'm a complete newb to the kj

No
is the short answer
How many miles on the Rustys?
Is it the full spring lift ?
If the springs are newer then you would have way too much lift to run, 5 -5.5 inches
Now since the Rustys are rated same as stock and sag fairly fast, you maybe down to about stock height but if you install a Daystar with sagged springs then the coils will be rubbing each other or be what you call stacked

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MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited

I'm not sure how old the Rustys is, it came with the kj when I bought it, the old man I bought it from said there was a vibration in the rear so he took them off, not sure what that was about, but it looks pretty rusty, no pun intended so I'd say there at least a couple of years old.

He also did not know it had a auto locker in the rear, hence the jerk when you give it gas.

If the springs are so bad, can I not just mix and match the Rustys kit with some OME coils?

Since you don't know how old the Rustys kit is or the mileage I would just start from scratch and do a complete new lift. Why use old parts that may or could be worn out and then have to redo it
Full OME spring lift with either OME or Bilstien shocks will set you back 750-800 or so
Springs alone are 340-360

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MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited

Man that's a lot for a small lift, that's why I was just going to reuse them, if it's really bad I will just take them off and start from scratch

A lot for a 3-3.25 inch lift
That's cheap for a good quality lift with springs / shocks etc
For a Daystar lift with new shocks all around you would have almost that
Rustys springs are only rated at 310-320 lb same as stock, if they are used much at all they are toast.
Out of all the lifts I have installed on KJs only did one Rustys and it was sagged back to stock height in less than 15,000 miles or so

But its your time and money
Good luck just trying to help and save you some in the long run

_________________
MUDD'S MOTORSPORT'S We do IFS lift installs ,
03 OVERLAND EDITION /Kilby-Skidrow-Mopar-4XGuard skids/ 2.5 inch TOTAL CONTROL JBA coilovers -JBA Arms/MOABS-31 FALKEN WILDPEAK AT3W / 4.10's etc, 04 Kilimanjaro Edition loaded, plus 05 KJ limited

Well expensive compared to say a tj lift, but anywho I will see what happens this week wether or not I'm going to order a new lift or not, thanks!