BlownB210 will confirm or deny, but I thought that this engine was for temproary use in occasional club fuel economy trials, so it would take a very long time to recoup the expenditure on fuel savings.

While sodium filled valves are wonderfull in extremely high heat applications, like the truck engine I described earlier, or in blown/turbo applications, & haven't yet caught onto how they would help to extend the distance traveled on a given quantity of fuel.
Lean mixtures burn much hotter, but at the low engine speeds & low throttle settings that are envisaged, exhaust valve temperatures should still remain well within limits.

While the suggestion is to push the 'static' compression sky high, in reality this is really just a number. The actual compression ratio/pressure that the cylinder sees is dependant on many things including valve event & the actual volume of gas in the cylinder [% of cylinder filling] If an equivalant of 8 or 9 to 1 is achieved in economy cruise mode, it would be way above what a stocker would see at the same manifold pressure. [That's 'pressure absolute' or pressure above zero]

I don't know how much benefit that taping over the seams would provide as economy runs are usually done at surprisingly low speeds to minimise the parasitic drag. This drag, & therefore the power required to overcome it, rises exponentially with speed.

Double the speed= 4 times the drag & the power [fuel consumed] needed to overcome it rises sharply too. Slow is economical, ... within reason, so tape over the seams may not provide much of an edge, if any.
The heat output from an engine that is producing the minimum power needed to keep moving should be well within the cooling systems ability to cope, even with the bonnet/hood fully sealed with tape as most of the air from the engine bay passes under the car anyway.