I found the spec for my 56 listed as a dwell angle in the electrical book.
On the 235 .016 used and .019 new.

Here is a link to Classic chevy, where I got mine. This link is for a 42-46 years, http://www.classicautopartsgroup.co...&action=detail&item=PBK-440-4246
Never can have too much info.
Brad