Want to see video output realtime on a projector

"In the old days..." I used to make videos in Motion where I could output the canvas, well actually the video output, to a video projector. Made all sorts of tweaking in situ easy and fun. Newer versions of Motion don't have this ability I understand. But I thought there was a way of using a AJA or Blackmagic box to output the clip into a projector. Just can't find any info on that process... any advice greatly appreciated!