I also had slight valve timing issues in my 98' Seicento (rough idling and hesitation) and the flat spot you also are noticing is a sign of too little valve overlap because of excessive valve clearance. However I went for bottom torque, so I swapped my cam for a 2000 Punto one (4X4 stamped in the cast), which have less lift and overlap by design, for fuel economy. I got a second hand Punto head for cheap and that had its own set of shim discs and with16 to chose from I got the valve gap close to specs (0.20 and 0.25). Valve seat material is not that great on the Fiat Fire engines, so you might want to take your head to a specialist (Wow, what a pun!) As the valves are in-line under the cam shaft as on a motorcycle engine, machining new valve seats only requires a single pass, so it should be cheaper than usual to have it done. You also have pitted valves as your car is 21 years old as mine so order a new set of valves when you have your seats and valve stems done. Otherwise got the exact same vintage as yours: SPI and cable driven speedo! Timing belt setting is easy on these engines and you got it correctly by the sound of your test drive. I usually use a mirror to be sure I'm watching the mark on the cam wheel head on. Also get an air filter, it hurts watching you driving around without one! Also Teenage boy exhaust routing! A new complete exhaust is cheap. Looking forward to your dyno run. If you have your head off, take off 0.1 for 5 extra HP.
Ron Simpson I have been watching some of his videos today, they are very good. Need to watch the coilover one as that’s what I was considering doing next.