Chevy vortec heads are one of the best iron heads you can get your hands on. But you would want to put on a vortec specific intake manifold as well. There are a couple of manifold-to-head mounting bolt holes on each side that can be redrilled at a different angle on a non-vortec manifold so it can bolt up to the vortec heads. But the ports don't match up vertically between the two.
Another option would be to find a pair of 305 HO heads. Those don't have the intake runner restrictions that your 305 heads have. The HO heads would be a simpler bolt on and go swap.