Hi all and thanks for the comments and suggestions along the way, much appreciated.
Grab a coffee or beer if you want to digest this in one sitting! This one is a long-winded recap/update on sorting out the generally poor quality Lexus/Toyota V8 engine swap into the LJ70 I bought, along with the 'overfueling' problem, whereby I stab the throttle a puff of smoke comes out and the plugs were fuel (not oil) fouled, along with a strong fuel smell, not surprisingly... Also the motor vibrates/misses every so slightly, Lexus V8 should be silky smooth, feels like a weak/dead cylinder, but unable to pin it down (see below). Anyway...
So far over the past 3 or 4 weeks I have:
-checked all wiring from the ECU to various sensors and earth connections (about 3 times!)
-figured out how to pull codes direct from the ECU with a test light (get an LED one, much better, less draw)
-added a missing O2 sensor to the left bank of cylinders and replaced the O2s on both sides.
-ran jumper wires from the sub-O2 pins on the ECU to the front O2 pins, (so the ECU thinks I have 2 pre-cat and 2 'ghost' post-cat O2s!)
-checked for vacuum leaks (none detected)
-cleaned all plug connectors and earth connections on the motor and chassis
-replaced spark plugs
-ran a compression test twice (all at 175psi, thanks god, except one cyl a bit low, c.155-160psi, but think it was washed down by petrol, checked a bit higher later on, but hey, it's a 21 year old motor after all)
-I noticed the piston tops were really covered in carbon, so I did a throttle body clean (also filthy) and did the old water injection trick while it was running to steam the intake and cylinders (works well actually, kinda like seafoam, but free!)
-Pulled idle air control valve, disassembled and cleaned, and reinstalled
-pulled each plug wire one at a time to see if I could detect a weak/dead cylinder - nothing convincing here, all dropped the engine speed, though not equally, and there was still a vibration from the motor c.1500-2000rpm
-chased down an annoying pre-O2 exhaust leak, a big no-no as it sucks in air and throws off the O2 reading (culprit was a pinhole in down pipe from welding) put putty around it and wrapped that side of the manifold/downpipe in heatwrap/stainless cable ties to give the clutch slave cylinder a break from the heat.
-adjusted throttle position sensor, erm, by ear! (will do this properly later on with a feeler gauge)
-fixed two pin connectors to the ECU that were not connecting well. I started the engine and grabbed the wiring harness and shook all the wires and connectors inside out and got a relay clicking like mad, a good way to find any lurking gremlins!
Well, its running better, but still a bit shaky and not what I would expect from the Lexus V8 in top tune.
My new plug wires, dist. caps and rotors arrived Sat am, so I put those on, wires first, just to test, no discernable change, so pulled the dist caps after a lot of grief and strong language got them out. Whew. (the covers are a pain on these).
The rotor arm and cap on the left bank of cylinders was awful! Surely this was it! The right side dist cap & rotor was better, but still pretty grotty. I am convinced these are original 1995 parts. Good bye and thank you for your many years of service!
Well, running a bit stronger, but not exactly as I hoped, so running out of options here. I sensed that the spark was not as strong as it could be, so I began to check the igniters.
Turns out apparently the igniter bodies need to be very grounded to the chassis, and I was not thrilled with the mounting job the shop did from the engine swap - lots of corrosion and paint between the bracket and the igniters. I tried to start the engine with them unbolted and it wouldn't fire, at all. I then loosened then while running until it started to cut out, and have to say it mimicked very closely the rough running I experienced...!
I sanded the contact areas to bright metal and reassembled everything. After letting it warm up, it seems to rev smoothly and very strongly and no smoke that I could tell! Usually there would have been a good blat out of the pipe with each stab of the throttle, but I only got a good shot of steam from the motor warming up. Once warmed up, it settled into a low smooth idle, about 500-600rpm (by ear), right where it should be, and having a good sniff of the exhaust (an acquired taste) it seemed much cleaner, mainly a bit of moisture still burning off...
In the end I think the lack of smoothness and overfueling (or under-igniting) has been due a little of everything, missing O2, weak grounds, weak connections, carbon build-up and soot, ignition dist/rotor/wire wear...ECU needing to relearn each time batt is disconnected, and lack of driving under a load!
So it's MOT time this week, it only has to pass the non-catalyst idle test, with a whopping 3.5% CO max and 1200ppm HCs at idle, no fast idle test...
Will let you know if it passes MOT, I've done all I can for now, fingers crossed!
Anything on two wheels being one of them. 
