Finally got round to writing the ending of this little success story..
First of all: thanks Bulls and Doug, could not have done this without your info.
@Bulls: the picture in the last post, what was it that I needed to see in that picture? BTW: I did double check the oil-channel thing on the head/rocker assembly, made sure I put it all in correctly.
So, managed to get everything back together. Was a bit worried if I had put the distributor in correctly, but after priming the oilpump (unplugged coil) for a bit the engine started right up, first attempt and was running smooth and with good oil pressure. I kept it at 2000+ rpm for about 15minutes to make sure oil was everywhere where it needed to be. Everything sounded perfect, engine temperature was perfect.
With a now warm engine I fine-tuned the ignition timing.
After this the first test drive: Running better than ever, pulls strong (for a 55hp V4).
Did a longer test run the day after and after approx 200km's I changed the oil + filter and put new coolant in.
Engine now also has hardened valve seats, so no more lead-replacement additives needed. All in all quite pleased.