You need to make sure that the bearing clearances allow sufficeint oil flow to cool the crankshaft and valve springs at substained RPM like the roundy rounder motors do and make sure the oiling system has enough oil volume in it to not allow the oil pickup to suck air at any time Many of these mods where done to bandiad the original problems, not enough oil volume in teh oil pan, hence the addition of the Accusumps and other pressurized external oil reserviors I'm not a big fan of the 1/2 inch oil pickup mods on any of my street and strop motors, but I don't run the motor at or above 5000 RPM for more than 30 seconds either
I do remeber being passed on the Autobahn by a Mercedes with a BMW on it rear bumper flashing it lights at or above 130 MPH back in 1968 near Frankfurt and Hanau Crazy bunch of Hermans