NO. The 318 will require special mounts or a V8 K member too.
Try really tuning the /6. a '71 should have a solid cam. Run the valves, do a full ignition tune-up and check out the carb. Change the filters. Also make sure the exhaust isn't plugged.
Empty out the interior and trunk of extra junk, get an alignment. Run the tires at 35 PSI.
Have you changed the ATF and rear lube?