After creating a 2-dimensional Conway, I went about trying to code a 3d conway in Houdini.
Using the nearpoints function within Houdini I was able to obtain all the neighbours of the cubes within a given radii. I then applied conway’s rules with some adaptation within the solver node.
(Vex node on prims)
int prims = nearpoints(0,@P,chf(‘vector’),chf(‘searchradii’));
i@neighbourPrims = prims;
//  nearpoints(int opinput, vector pt, float maxdist, int maxpts)
// or if you want to not store itself:
i@neighbourPrims = prims[1:];
//Prints the size of 1 instead of 4
int length = len(@neighbourPrims);