Re: Chain tensioner
To be truthful I've never used #410 chain. I know some do and swear by it but I've had good luck with #41, never had an issue with it and never felt the need to experiment otherwise. I use a good quality, Diamnond or Morse industrial #41 and it has served me and many other builders well.
As far as the tensioner bracket goes, We always suggest to make sure it can not loosen or rotate on the chain stay. The taper really shouldn't effect the clamping action but I happen to be a firm believer in securing the bracket by some method that doesn't completely rely on the clamp method. I'll open a can of worms here by mentioning some ways to do that so I won't but I'd suggest you do a little research and read the plethora of information that has been posted here on the pros and cons of the infamous chain tensioner. Just type in 'chain tensioner' in the Google Custom search then sit back and read. Most important; do what works for you, never mind what others say to oppose your ideas.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"