i've seen conversions done with mis-matched AFM's. that will dramatically alter fuel
changes to the water plumbing circuit can upset the ECU temp sensor. it constantly thinks the engine is cold and adds more fuel. however, I cant imagine its that out it pumps out neat fuel
i've never seen a dead oxy sensor make that much difference that raw fuel comes out exhaust. in fact, it cant because its only a trimming device. however, its more than likely "sad" at this age., and more so if its had lots of raw fuel around it. we are changing them all the time on 20V engines
if it really is pumping out raw fuel, i would also suggest a careful look at injector performance., a faulty ECU could be holding 1 open or 1 could be physically damaged.
any competent mechanic will be able to do the basic diagnostics but few will have any interest in checking the details of the conversion. if you do no good down your way, i'll be happy to look at it after the 13th. message me to make a booking