rear chain noise on 2002 4.0L...chain kit or used motor
 

Well my wife's 2002 Explorer XLT 2x4 4.0L with 197K has the rattling coming from rear of the motor and has been diagnosed as worn rear chains/guides

Dealer wants $3000...Pfff not gonna happen

Indy gave me 2 choices:
1. Parts (chain/guide kit) & labor for $850 but he said he's done it before and it still had the noise so he said he can't guarantee the problem will be gone.

2. He'll source a lower mile used motor and swap it in for $450 + cost of motor.

they both seem like a gamble so I am turning to you guys with experience, which way would you go? Bare in mind I know most will say to just get rid of it, but with the kids in private school we can't afford another car note until my Audi is payed off in 2 years.