I did the cross over on one, cant really say it helped
much... but the biggest thing is to drill the ports
to 1/2" like said above... I turn my engines up to at
least 8000 and more... I did have 1 engine failure
but it broke a rod(stock type rod) and it wasnt a
oil failure... at 7000 rpm you dont need to do much
EDIT
and drilling the mains with the 9/32