Welcome to the site, Eugene. Check the ground that Mike mentioned above. Also check to see if the body ground wires were hooked back up after the engine swap ( common mistake). They run from the back of the head to the firewall. Look for a braided wire. If that doesn't help, push in on the lower right corner of the gauge pod- that's where the connector is and it can get loose. If pushing in helps, even for one of the gauges, then it indicates that the connection is weak and needs to be cleaned/tightened. Let us know, and we'll get you info on how to fix it.
Temp gauge might just be that it is not hooked up. Look for a single green wire between the #1 and #3 spark plugs ( on the driver's side). Gas gauge could be a bad sender or bad ground by the gas tank. Speedo is mechanical, so no electrical gremlins here. Could be it's not hooked up ( check rear driver's side of the trans), cable broken, speedo gear stripped.
You'll probably have to end up tackling each of these as a separate problem. That's part of the fun of owning an old car- learning new stuff, getting the satisfaction of finding and fixing the problem, and having the knowledge to fix it or similar problems in the future. Enjoy the adventure:nanawrench: