Between the two cams (the Howards and the GM) I would go with the Howards cam. I haven't been able to find the advertised duration for the stock Vortec cam, but going by the degrees on the ramps on the GM cam, I believe the Howards cam probably has smaller advertised duration even tho it has more at .050" lift, so I think it will give more low end torque and still give more topend too. If you were of a mind to change to a hydraulic flat tappet I would have to give serious consideration to the Summit K1103. It's Summit's version of the grind that GMPP uses in the 350HO 330HP crate engine with Vortec heads (which for practical purposes is your Vortec engine with a flat tappet cam). It has mild street manners (idles well with plenty of vacuum for power brakes), has a noticeable choppy idle, and pulls well.
Here's a Chevy with the K1103 cam.