Originally Posted by Dan Burkhart

The brake arm can be re positioned any way you need it to be. You may get lucky with chain length and get close enough that you don't need a tensioner. I've managed this a number of times, most recently on one of my own IGH conversions. A half link chain or even just a half link connector improves the odds. Sometimes, changing the cog up or down by one tooth makes the difference.
A bit of chain sag is acceptable provided the chain line is good.
Also, there are no turn washers specifically for vertical dropouts. They engage the dropout better. https://www.sjscycles.co.uk/hub-spar...ropout-hmw534/