Okay, here's the current state of affairs: each exhaust valve bent, tiny scratches on the pistons, cylinders like new.
Chain blades okay, tensioner okay (1/2 engaged), sprockets okay, crank sprocket key okay (it's huge actually). But there's uncertainty about the chain: it measures 5mm short of the replacement limit, 145.82mm actual length across the 0-23 links with 13kg attached, vs 149.48mm, which is basically a full chain link.
Apparently, there are two versions of them cam chain, and obviously I already have the newer one with 3/4 blades per link compared to 4/5 blades. So, is the measurement of the service book with 149.48mm still correct?
The question why the chain jumped teeth, is still unclear, unless the service book's measurements do not correlate with my chain...