Well, it turned out this didn't cure it after all (nevertheless worthwhile to check though). Despite I had run a few tests up and down the highway without any issue the problem is back again. The week after I had done this I drove my car to have the valuation report redone for the Insurance company. Only just a few miles away it started to play up again just as before. Sigh!
By now it was also time to get the bi-yearly MOT done. Plus it did require a proper 10k maintenance check up to be done. I have driven a problem free 10k kilometers untill this nasty issue popped up out of the blue. Initially Stefan, the mechanic, stopped doing any activity as he's planning to move out of the Netherlands. But since this turned out to be more problematic as anticipated he's staying a little longer and as such could plan in limited additional work. So I consider myself Lucky as he could look into this issue and also perform the 10k maintenance interval which does include the valve check/adjustment and distribution chain check/adjustment (if needed) and the fluids, filters, etc.
He suspected an ignition issue which makes more sense. As he has got the required test equipment he easily could check out the distributor. And it became apparent it was problematic indeed, see for yourself:
And a small video on how it should be:
The root cause turned out to be a flaky capacitor - Sigh!
So I had to look up the correct type and model used. This particular item was not listed in the part manual.
But further checking online revealed it was the following: Magneti Marelli CE29T part nr 56181116 and 0,25 uF. It's been used on many Ferrari's (likely other Italian brands as well). And for the records, the distributor is a Magneti Marelli S138C
Since Stefan had done already many electronic conversions he did happen to have a good capacitor on stock of the right type. Also the contact points got replaced and all was tested fine. Additional a test run was performed and no more hiccups were experienced. Phew!
I'm glad it did not require an electronic conversion as I like to keep car Original as much as possible and besides it's a very costly swap.