57LSUK

I have a 57 Chevy with a recently completed LS1 Transplant complete with fuel injection from a very low mileage 2002 WS6 Trans Am.
It has original Manifolds home brewed exhausts (no cats) and original oxygen sensors in same location as original.
ECU was set up by now defunct Arizona TPI.

Car runs quiet and super sweet how ever on maiden voyage noticed hesitation at low steady speeds of approx 30-40 mph and it felt and smelt rich.

On replacement of plugs on drivers side of engine (LHD) they were ALL heavily sooted yet passenger side fine.

No immediately apparent loose connections or pipes.

Unable to take another run since changing plugs and leads due to torrential rain here in UK at the moment.

I was leaning towards oxygen sensor next.?

Any thoughts much appreciated.

Thanks in advance