Thanks again for all the help.
At the end I ended going for the E61 (all the fuss for nothing). I found it for 110 Euro from an italian reseller and from an italian manufacturer. It was the last one and now they are out of stock.https://www.cis-spareparts.com/en/coffee-machines-spareparts/single/group-heads/133000.html
At that price it was simply a no-brainer
based on the little I know.
I also found this chinese manufacturer, but they had no interest on selling me just 1 unit. They have pretty neat boilers tho, but they stopped replying me when I said I wanted to buy only 1.http://www.chengtaimetal.com/pro.asp?op=2&anid=81
I am in search for a 1L boiler, I can find lots of big boilers (10L ish), but the smaller boilers are a bit tougher to find. Going to visit a local coffee repair shop today and see what I can scavange