Just another data point:

I always return to South America with two large duffels that measure 36 X 17 X 17 when packed full. I have never been questioned by a UA or COPA agent about length. I have never pushed over 70 lb., though.

This is on about 45 check-ins over the last 3 years. These are all flights ex-USA. I don't know that I would count on agents in other countries doing the same. IME working with people in my company from other countries, I often see a business culture where functionaries strictly follow all rules.