You could be right of course, frankly I don't remember exactly if we took that engine apart or if it was the block still in it and the head separately. Either way that piston must have collided with something at high rpms and yes it looks like a valve. As soon as I recover the head I'll let you know if a valve or two are missing :)
I built my engine in such a way that the valves clear the piston even when fully opened at dead center so even if my belt rips and the timings are messed up there won't be a collision. The only other mechanical collision could happen if a rocker arm disintegrates so I put in the reinforced stable to 7500rpm ireland engineering ones and trust they won't break :).
Are you planning to tune the engine also if you are going with racing rockers?
It is, I rebuilt it completely losely based on the Alpina C2/2 2.7L M20 engine only I used a 272deg Cam and they used a 268deg. Check my post here:
https://steemit.com/cars/@peterschroeter/7-years-in-the-making-2-rebuilding-and-restoring-a-30-year-old-bmw-twice
The rockers are mostly preventive as I haven't pushed the redline in the ECU, it's still around 6500rpm but I figured better safe than sorry. The cylinder head is really overdone for this but at least I know it's solid.
I love your car already :) Few years back we were working on 1991 320 IS. Italian version of M3