85 is pretty big, I've checked a 65 before albeit in Y. It was full though.

Best case you'll get some looks at security, and you'll want to tape those straps down well. Definitely make sure that day pack is accessible in case they gate check it.

My gut is if you get it past checkin (OLCI is your friend here) and past security it'll be fine as checking backpacks even strapped down normally requires a large bag (in my experience)

You need large bins too, any narrowbodies on a segment and you're going to have issues I fear. 787s in J and you should be fine. It's the people who turn up with 6 bags or in Y that tend to cause issues.

Let us know how it goes, I've always wanted to try taking my checked luggage on a wide body J intl just to see if I can get away with it