If you're not checking bags, then 1:36 E international to C domestic connection is likely doable, but could definitely be tight depending on circumstances. There are a lot of variables that are going to be hard to predict -- a delay in your BA flight, some sort of backup at customs & immigration or a backup at security could all throw a major wrench into this. My last few arrivals in Boston from London I've been through customs & immigrations in only a few minutes and it's never taken me more than 5 minutes at security in terminal C. However, I have Global Entry and therefore TSA Precheck, so that I get bypass the regular line at both customs and security. But even without GE, the lines at customs & immigration were not long at all. Then again, I've also seen where the lines are all completely backed up. I will defer to people who have done this recently, because my experience with international arrivals is at least a year old at this point.

With B6 you can also pay for "Even More Speed" which gets you expedited security in addition to priority boarding, but you have to go to security at C land-side to take advantage of that.