i know quite a bit about this engine
and its limits
spec on my head is
diy porting done by myself way over size
supertech bronze valve guides
Ferrea Racing +1mm valves (inlet and exhaust)
supertech smaller valve seals to suit the valve springs
supertech 94lb double springs with titanium retainers
uprated upper front guide bolt
including when fitted was a cometic gasket and arp head studs
balancer shafts deleted for use above 7000rpm