10" outlet off of manifold?

Getting ready to finally set and seal the barrel system on my 8" RMH. Would it be better to start off with a 10" outlet off the bell chamber, then reduce it to 8"? I have a good 6" clearance at the widest point and 3" at the narrowest in the bell, and 5" from the heat riser to the barrel lid. Or would it be better to leave the whole exhaust at 8". I hate to experiment with the 10" and not have it work - then I'm out $70 with not being able to return it. Anyone have any thoughts on this? Any advice would be appreciated!

pics!

Sorry, will try to get some pics of clearances and the proposed exhaust outlet. I read about this on donkeys forums and it seems like starting with 10" might be good, but I'd hate to do anything to jack up my system and make more work. Has anyone tried it this way?

if it's like this pic. Yes.

That's a 8" to 6". So a 10" to 8" wont be a problem.

better too-much then not enughf
too much it's unnecessary. not a problem