It is possible to put Vortec heads on a non-Vortec block, but it is not recommended. The main reason for this is that the two types of heads have different valve train geometry, which can lead to compatibility issues. Additionally, the Vortec heads are designed to work with specific intake manifolds that may not be compatible with a non-Vortec block. For these reasons, it is generally advisable to stick with using Vortec heads on a Vortec block.