Welcome to CHR! Any flexplate that meets SFI specs would be a good choice, Summit, Speedway and a lot of other online stores sell them. Count the teeth on the ring gear and be sure to get a new one with the same number of teeth. As for the torque converter you should replace it or at a minimum flush it thoroughly before installation, wouldn't want any old contaminants getting into your new trans. If you go with a new converter, be aware of the advertised stall speed of the converters you consider buying a stock converter behind your stock engine should be fine, or even a 2,000 RPM stall speed converter should work well. Might want to also get some input on your converter selection from whomever does your transmission, sometimes a trans shop has a good source for converters and it's always good to get their recommendation on what converter would be best with the trans they build.