Such dangerous words, "I have heard".

There were 383s built with cast cranks, I would tend to put them in 1971. One can tell how an engine was built by looking at the engine ID pad. If there is a letter "E" stamped onto the pad the engine was built with a cast crank. Of course this doesn't include 1969 model year engines that have their engine code starting with "E383" or E440", because there the E is for 1969. But if your 383 has G383R____ E
on the engine ID pad it's a 71 model year engine that came with a cast crank.

Cast crank 383s, 400s and 440s all used the same external balance weight amount.

R.