Parts supplies are constrained industry-wide at this time due to world conditions. Because of this, some parts will take longer to get.
Cam, Valvetrain and Lifters
Design Factory Artwork
K & N
With an automatic transmission, the shift point will determine how high the engine revs, probably to slightly less than 5000 rpm. With a stick, you control the shift point, so it could conceivably be higher. Most stock engines aren't going to get past 5000 rpm though due to valve float. The stock springs can't keep up when the valve starts opening that fast.
With good springs and more cam, the engine should be good for 6000-6500. I know of one engine in a road racing car that hits 7500 rpm on long straight aways. Not a good idea for a street driven car though!
I could've responded sooner, but thank you. I'm trying to persuade my uncle in getting a project car for us, and I want a 6cyl biased of its possibilities.