Shaving the head by a large amount isn't necessarily a problem in and of itself. It's the flow-on effects that need to be considered.
Foremost and obviously, intrusion into an oil or coolant passage is an issue as might be the thinning of the available material.
Currently, an oil channel and a dizzy height issue has been observed.
There's also the possibility that the rocker geometry might need height correction via shimming. This is a common practice for competition engines.
Given the head is effectively lowered and the cam has remained stationary, an issue might be found in that the cam will now have inevitably altered timing. This is commonly addressed via an adjustable cam sprocket.
It might also be that the tappets now need to be recessed into their bores so as to recover stock clearances to the cam lobes.
And the use of Lotus 821 pistons might not be automatically detrimental overall, but you'd need to get the unit on an engine dyno and be able to compare it to a known spec before anyone could say anything significant one way or another - not terribly practical for most of us.
The stock Lotus CR was 10.25:1 if I recall.
That said, I'd also want to know if the valve reliefs haven't come too close to the top ring. Visually, the valve reliefs look to be significant so I wonder about the extent of cam lift.
Lots of things need to be measured & checked when radically departing from the safety of a factory spec. - you pays your money and takes your chances but none of this is the end of the world IMHO.
My $0.02 worth, anyway.