Using the flexplate snewpy said will work but if you want it to be perfectly balanced just take your flexplate back to where you had ithe engine balanced and they should have the papers on file where they balanced your engine and can check it and correct it if it's off. A buddy of mine did the same as your doing. Had an engine balanced for a manual then bought a different car with an auto and he took the B&M flexplate back to the shop to have him check it. It was close enough to work ok but to make it perfect he had to add a little weight.