90 XJ - what do i offer?

hey guys. theres a guy in my town who selling his XJ (make me an offer) -

he's got bushwhacker flares, a rubicon 5.5" lift kit (short arm), 33 bfg mt's with decent tread, 4.56's and a rear locker (dana full floating). the engine isn't running right now (knocking bad).... i

Im just wondering what i should offer him for it. im planning on pulling the off-road parts and putting them on my rig. im not really sure how to value used aftermarket parts, but i think that these parts new would cost me about 4 -5 grand

thanks for the help

how the rest of the jeep look besides the offroad parts?
engine milage? axles?

I'm sure that would all play a part on what he wants to hear...

or just talk to him and ask him the lowest that he'll go...
\just my .02