I'm no expert, and after consulting a few the two
non-std things I did are:

1) cut a slot in front of #5
http://rob.com/lancair/2003.08/DSCN6346.jpg

2) cut a slot in behind #2
http://rob.com/lancair/2003.08/DSCN6345.jpg

the idea is to get air around the cyl where the ribs
become short.

my notes from the APS class have Walter claiming most
of the air escapes from the top cowl via the prop hole...
but I can't see that as an issues in the lancair design..

once the gami spread is minimized, one knows the torque
between cyls is minimized, so the CHT delta is cooling
air imbalance between cyls.. so its not necessarily total
air leakage, but directing the air you have evenly between
all your cyls.. ie: direct as much air down your hottest cyl
and the others should be fine.

humbly,
Rob