In Sports Car Club of America Formula Vee racing (my other expensive
hobby) a few guys have tried updraft cooling on the blueprinted 1200cc
motors we use, which put out about 60 bhp, have no cooling fans and
are run at full throttle (except for brief braking) at average speeds
in the 80-90 mph range; we also run in drafting packs which put a lot
of hot air into every motor except the one in front. Nobody has stuck
with it; they say that the cooling drag is not reduced measurably (if
at all) and the heads run about 20-30 deg F hotter than with downdraft
cooling.

Your figure shows a low-pressure area on top of the nose. This is
substantiated by the placement of the cooling outlets on Peter
Garrison's updraft-cooled Melmoth II; they're so far forward and so
close to facing forward that everyone mistakes them for inlets. Also
note the high-pressure area under the nose in the figure; the only
reason this changes to low pressure behind the cowling is the "chin"
at the cowl's bottom rear. This is not a natural feature; it has to
be induced with aerodynamic trickery at some cost in drag.