1991 Dodge Stealth Replacing O2 Sensors

I had a full tune-up, plugs, wires, air filter, oil, etc performed Apr. 2008. About 3 weeks later, RPMS would fluctuate, car would "buck" and stall. Exhaust checked. No leaks. All scheduled maintenance has been performed on this "NA" vehicle. My import mechanic with 35 years experience no longer contacts me. NO, he would not have done anything to harm it. Bottom line. Where are the o2 sensors located? How do I access them? Bought (2) Bosch sensors and was told @ $300 for shop to install. Another mechanic friend is willing to install them; but first I would like to know where they are located. A pic would be helpful. I cannot afford $300 repairs, as a single mom with no income (pending disability). All plug wires are in proper order. Have had plugs changed and wires replaced at the same time twice.
I keep a supply of Plenum gaskets for accessing the rear bank. Replaced entire coil pack assembly. Got that at no charge (Mitsubishi OE). I have come to the reasonable conclusion that the o2 sensors are the problem. Excess fuel consumption, plugs being fouled due to excess carbon, fluctuating RPM's with "bucking" and stalling. No signs of Catalytic Converter problems, yet. I use all OE replacement parts, except for some crappy Taylor plug wires. Now have OE NGK plug wires that will be installed upon next plug change. PLEASE HELP! Cannot find anything online to tell me where the o2 sensors are. Yes, always premium fuel used per manual states MIN.
93 octane. Original plug wires were still in engine when changed Apr 8, 2008. HELP! I cannot get to stores for meds, groceries, etc. There is a slight ticking noise. Car runs fine for @ 5 miles, then acts up again, same problem when it gets hot. Plugs fouled and "bucking", stalling.