Rebuilt engine: cranks but lots of white/grayish fumes

So today I cranked the engine I was rebuilding (Skoda Estelle/120 ’72, RWD, rear mounted engine) and while it started, yes, but not without some struggling, I got a lot of white or light grayish fumes. I first did a crank without water, just to see how it goes, and got this kind of smoke but very subtle, out of the water pump and thermostat casing. I guess it is just paint, mounting oil, etc being fried. So the next crank I put the out hose into a bucket: I didn’t get bubbles, so I guess compression is not going into the cooling system. But I do got lots of smoke.

I could inspect the chambers visually by looking through the sparkplugs holes: I see some oil there. I wonder if this is because the rings, or it is because I may went too happy with oiling the cylinders when building the engine. In any case: light gray fumes.

Sparks 1, 2, and 3 got a little bit of oil, park 4 got a lot of black carbon. Oil pressure at ~1.500 to ~2.000 rpm is between 4-8 kgf

So: rings? lean carb? mounting oil? wrong timing?