[Hippie]

I have a Cadillac 4.9 V-8 ( NOT a Northstar) I am using in a swap project and it has a TON of low end torque right from an idle but is all done by about 42 to 4300 RPM. I need just a few hundred more RPM and can afford giving up an equal amount on the bottom, I have the torque to spare and the gearing to make up for it. There is NO aftermarket for this motor but I can get the cam reground, however due to it's configuration even a modest increase in cam lift creates the need for very involved and costly cylinder head and valvetrain mods which I'd like to avoid. Would a duration increase of around 6 degrees without increasing valve lift gain me anything ? How much shift of the TQ curve in the RPM range might I see by retarding the stock cam 4 degrees ? Thanks.