I am curious, to the OP, what width are you most comfortable riding now? Or did you already answer that with 44cm? If 38s are too narrow (and at 6'5" they are for me), how have 40cm or 42cm units worked? That question comes from seeing if splitting the difference nets you a better outcome while still flying under the radar with purists (of which I know none, but I'm not exactly a social hub here).

Another idea and question, given that riders often upgraded their bikes throughout the years, to one degree or another, what is your personal year cut-off for "period correct"? Many bikes in the '70s, as far as I can tell, shared many design features, especially in the early to mid '70s. So something from 1978--within five years of your bike in question--seems well within period correct to me, and thus you could run wider bars that were now an option (but the same model available in 1973, like Cinellis). Things really changed in the '80s, so to me, that's where the range of period correct years gets narrower vs. the '70s. I tried looking up Cinelli bar model production, and didn't find anything (let alone don't much know where to start besides a search engine).

I/we understand your quandary, but we also want you to ride and enjoy your bike(s)! If you can find a wider bar that fits the stem on that bike and looks like it belongs in that era, then I say go ahead. Some guys like wall art, but it sounds like you don't want this to be (hooray!). If you can find bars and models that got to 40cm or even 42cm in 1973 or within a couple of years, keeping strictly to your period correct requirements, then godspeed on that search and may the internet and BF C&Vers bear fruit. Otherwise, we have choice and better technology now, so taking advantage of that is ok with me.