Got the same cam in my 340. High idle is the only way to keep it at a stable RPM. This cam makes only 9" of vacuum. Also, calling it a 280 is misleading. It's really 288 @ .006", which is the SAE way to measure seat duration.
I've said it before and I'll say it again. These MP cam designs are dinosaurs and you can make way more power with better driveability with a modern grind.
