1985 Questions for all other cars Ferrari 308

I own an older, but late model, Ferrari 308 QV. Lately it has been difficult to start despite what has proven to be a fairly reliable fuel injection system. I've had to pump the gas a few times, but it eventually turned over and ran normally. This past weekend, after going to a car show, the car backfired for the first time since I've owned it. Today when I started the car up again, it's power was noticibly anemic and it repeatedly stalled. Which it's never done. On further inspection, there is a strong smell of fuel after the car is shut off which leads me to believe that I have an entire bank of cylinders not firing and I'm pooling fuel. In the Cat Converter most likely. How can I tell which set, if either, of the cylinders are not firing and where do I begin to diagnose this? Yes it's a low milage car, but it's almost 25 years old. Last servicing was 2 years ago and the plugs and their connectors look ok. Thanks.