Outer Limits 4x4 Board

i am looking at putting the racerunner 18 travel 2.5 OD coil overs in on all 4 corners but have no idea what spring rates to run i plan on using the dual rate kit it for my GU 4.2td the battery and radiator are going to be mounted in the rear

Have you looked into the non coilover sort?
The should be cheaper due to less components, but you would have recharge with nitrogen if you were to play with fork oil levels or viscosity.
Or are they nonsuitable for a road car?

pretty sure that air shocks won't be able to support the weight and the air shocks aren't flash at speeds i think

currently running the 2.5 inch fox air shocks there fine on road in the rear just a bit rough have done about 40000klms was just looking at going to the next stage and to look for more travel as they only come in 14inch long but will probably put them in the front just doing some resurch first

need the unsprung weight, sprung weight front and rear and you can workout from there a bit easier, no point in geussing, try ABT

Our Fox triple bypass install kit will also mount coil over in the rear, but the front not enough room, we normally use 10" front and 14" rear, using all the stroke both ends, with 40mm bump spacers and we use a 3" lift spring with extra long free length to stay captive, or a 6" lift spring with that travel, which max's out standard steering arm, and control arm travel with those lengths.

Coil overs dont give you the adjustability on valving without dissassemble and revalve issues.