SBC Exhaust Upgrade, stock VS modded engine
 

I know that exhaust on a stock 6.2 doesn't really give a whole bunch, but what about exhaust on a moddified small block? I am about to put on a set of these:
http://www.keitheickert.com/detail~ID~2909.aspx
on my built 383's. I'm just curious what to expect. I went with GM performance bowtie heads, and 1.6 ratio rollers, wtih a bunch of lift, so I am flowing some air in. (Sorry I don't have the specs in front of me) I GPS'd at 67 MPH with 4 blade non labbed props only turning 4900 rpm's. My goal is 70 or better. They are going to be installed, retuned, and dynoed at the same time by Bob at Full throttle marine, (great guy to deal with BTW). After the exhaust I am wanting to labb the props to run at their peak. What do ya'll think is realistic?

I have a set of Revolution Marine's exhaust on my 406 SBC, and they work great.

Chris