hi need to say what size engine - although XL only had 2 - 170 and 144.
not definitive answer but here is colour (60's technicolour) for the XP engines rockers and aircleaners (144,170 and 200)
http://xpfalcon.kicks-***.net/XPFalc.../1-Engines.htm
although the 170 is more red than this photo
and the xp's had silver blocks whilst the early falcons xk/xl ( and XM ?) had the silvery green ones mentioned by redxm.
if you call earlybirds at thomas town ,vic i am sure he can tell you a rocker /aircleaner/block colour match.
i saw an XM engine they had recoed and it had been painted the silvery green block
pretty sure the 170 stayed red for rockers and aircleaner
and just to add to the confusion :my XK 144 has blue rocker cover and aircleaner:(hard to see -but you get the gist)
brett