Ford Repair: engine replacement, internal combustion engines, oxygen sensor

Question
James I have a 1998 Ford Explorer 4 wheel drive Eddie Bauer that I recently had the timing chain tensioner replaced on and now the engine runs really rough at low speeds but sounds ok at highway speeds and idles fine but upon hooking up the vehicle to a computer it will not read oxygen sensor info., says it is running low on one fuel bank and that it is cutting out on cylinders 2,4, and 5.  The only problem with the vehicle when I took it to the shop was the timing chain tensioner had broken and was making an awful racket because of this.  To let you know the tensioner broke when I started the vehicle and not at speed and was not driven after that to minimize damage.  I had another mechanic who put a rag over the tailpipe and said it was sucking and blowing exhaust and he thought it could be a bent valve but no one is for sure and I paid 1600 dollars to have the timing chain tensioner on the front of the motor fixed and now everyone I talk to wants to charge me at least that much or more to take the engine out without knowing what is wrong with it just to figure it out and fix the problem.  I am wondering I guess if I should let them have at it, completely replace the motor, or drive it till it blows since it already has 130,000 miles on the motor.  I am in college with a new child and new wife and really cant afford anymore 1600 dollar mistakes.  If I were to replace the motor as well- mine is a 4.0 litre V6 SOHC motor and are pretty pricey compared to some other motors of the same year.  I was wondering what my alternative for replacing the engine with a different size or style motor would be without having to replace the transfer case or tansmission since I already have replaced both of these articles on the vehicle at 60,000 and 84,000 miles respectively.  I am not a gearhead or amatueur mechanic at all but I do have an understanding of internal combustion engines and their systems and what they do just now how to fix them so anything you can tell me would be of great help and will be listened to and acknowledged.  Thank you very much.

Answer
The guy I carpool just had his Eddie Bauer jump time also.Price a motor at you're local parts store,but have new timing chain and components installed before you install the salvage motor.Most parts stores can get you a used motor with a 12 month warranty.I don't believe that the 1998 SOHC had the front and rear timing chain.However,the figures that you have given sound about right.Just to let you know,we parked his and he bought another car.If indeed one side of the engine is doing like you say,I would replace the engine.