Safe RPM for a 408" Magnum?

"It's a small block after all. If it can't handle rev'ing to 6500rpm when needed, something's wrong with it. Heck, I spin my 493 inch Mopar to 6500 rpm regularly."

Couple notes on that line of thinking... The 493 will have forged pistons, and the 408 has a longer stroke and shorter rod than a 440, or 383 for that matter. It is, for all intents and purposes, no longer a small block.