Video heads and clustering

Huh?

If I remember correctly, VCRs came with at best four video heads. Therefore, the limit to the number of video heads you could have connected to the computer would be limited by the number of analog video switches you can fit, combined with the signal degradation that would come from having too many junctions along the video cable between the VCR and the capture device. If you connect them to a USB video capture device, then the number of video heads would be limited by the number of devices a USB bus can address, which I believe is 127.

That is, unless you're asking something completely different. Your question is insanely ambiguous, as we can only guess what you really mean when you say "video head."

You can have as many screens on each node of the cluster as you can fit graphics cards on a PCI bus. The fact that it's a cluster of multiple computers is irrelevant. There's a completely different question of how quickly you can feed new data to the multiple screens, and that's limited by the bandwidth of the various busses involved between the source and destination.