The reversing element on openers is usually a spring-loaded swinging assembly that is activated by tension on the chain, so a reverse mount would still work, ie. the motor reverses direction whichever it is traveling when it encounters an obstruction. The electric eyes are a different proposition.
They make kits for low headroom that have a second horizontal track and different top brackets, but there are still a lot of interesting variations out there to make it all work. Just don't do anything crazy that ends up being unsafe.