I finally found my converter catalog. My wife put it up in my bookcase, not in my desk. According to it, from 1967 through to 1977 the 383 had a steel crank, which means no weight on the converter. There is no reason I can see, unless you're heading to an NHRA track where a SFI flex plate is mandated, that the stock mopar flex plate will not be suitable for your application. The stock plate was supplied from the factory for bigger engines with more HP than yours. There are 4 different stock flex plates: 2 -12" units and 2 -11" units. The difference in both cases is the mounting of the plate to the crank. You can have either EVEN crankshaft bolt holes, or UNEVEN crankshaft bolt holes. I don't know where you live in B.C., but send me a PM and I'll steer you to a place that can help you with your stock flex plate.