Yes, especially if you have a 4 speed or if you plan to race it with sticky tires. I would do it even on a stock motor if I was planning to run it hard. One time, I had both motor mounts break at the same time. That was scarry because my hood moved! What I have done for years ever since then is to take a stock set of mounts and carefully cut some 3/16" weld plates to fit between the top and bottom half of the stock mounts, weld them in place and paint them black. Do both sides and make sure they fit tight up against the rubber so they don't stick out. You can hardly tell they've been modified unless you inspect them pretty closely. I had a pretty radical cam and did not experience any vibrations or unusual feeling in the body from solid mounts. Good luck with it!Rebuilt my 383 with some upgrades. I have been told it should produce 425-450 HP. Will stock mounts handle this or do I need to upgrade the mounts ?