You say you changed the coils - were they Splitfires or similar, or 2nd-hand stockers? If the latter, it's very possible that one or more of the coils you've swapped on aren't working properly. If it is indeed running lean as you say though (measured, or guessed?), maybe you bumped an injector plug or crimped a line to the fuel filter or something, who knows. The timing might be out too, did you knock the plug on the CAS (front of the engine)? Stuffed AFM/plug? Plastic still on the fuel filter (have seen that before lol)
Does it have a consistent miss at idle? If so, assuming it's a spark issue, pull the plugs one by one and see if any are wet. If they are then your injectors are probably working fine and you've identified the cylinder/cylinders that isn't/aren't firing. Then it's a process of elimination... swap coils around and see if the problem moves with a coil for example, or whether it stays on a given cylinder, swap plugs around, check connectors, clips, earth straps, coil loom, AFM etc. If all else fails, grab a mate with a working S1.5/S2 33 and swap parts until yours runs properly and work it out from there.
Also, IIRC 6s are the stock heat range for plugs. I used to use BCPR6ES, they're coppers and are pretty cheap and did the trick nicely.