Carb issue - fuel in cylinders

OK... This has been a long wait. Shipment with spare parts took forever, then bad weather and busy work. Anyway - I got everything back together. New head gasket, piston heads cleaned, valves superficially cleaned (I did not remove them entirely), new distributor, some rubber replaced as well, new fuel filter. The car is running, and it does sound a bit smoother now
However, the power loss issue remained. My impression is that this happens when I drive at high RPM for more than a minute or so - so whenever I have to go uphill, after a while there is a sudden loss of all power. It does sound like there is not enough fuel, and given all your previous comments this is probably what I should check now, right? There was some debris in the fuel filter even though it has been in there only for about 500 km, so presumably the gas tank and fuel lines are just being cleaned and may block the flow.

... and another final update
It turns out the problem was not with the distributor. I feel stupid saying this now, given everything I have tried before checking this... The problem was with the flame trap which was completely clogged. I had checked the fuel flow when I redid the carb, and it looked ok. But I presume it really was just on the limit to not working any longer, and when I tested again with the restored carb, the flow was insufficient.
Either way, I cleaned out as much as possible (will replace it eventually) and I can now happily burn fuel again at will, and the car overall runs much better than before (i.e. no power loss at all). I still can't get it above ca. 85 kmh on a flat road, but I now believe this has more to do with the transmission than the engine. Even in 4th gear the engine runs at quite high rpm at that speed, and it does not sound like it could go any higher. Maybe it is common for certain models to have a transmission that would not allow them to go fast? Given that my car used to be a transportation car for fire fighters in a mountain village here in Switzerland, the emphasis may really have been on power, rather than speed - does this make sense?

In any case, thanks everyone for your input.


EDIT, regarding top speed
I found this thread
https://www.landyzone.co.uk/land-rover/top-speed-from-series-3.217996/
and it seems my top speed is perfectly normal, at least not off the charts low (even though I did not find any numbers for the 6-pot petrol engine there). Is this correct?