Design questions for for split barrel bench bell - input & exhaust, and bypass

I just recently did my first test firing on my RMH and posted results in a previous thread.  Many thanks for the online counseling for my meltdown, permies RMH hotline to the rescue!  I'm now proceeding with more confidence thanks to your kind input.

Next questions concern fine tuning my inlet and exhaust to and from the split barrel bench chamber, and designing a bypass.

First, the inlet and exhaust to the barrel, picture attached far below (not the inserted photos of fittings) .  My thought is that the two ports could use more separation.  I had placed a 24" section on the exhaust which fell off during installation (this was a mock-up for a test run, I would secure it w/ sheet metal screws for  permanent installation).  I could replace the 24" section, and/ or install a sheet metal baffle between the two.  Notice I have a brick under the exhaust, I could remove that to get it lower.  i could also squash the exhaust into an oval shape, like I did the inlet. just to get more height difference between the two.  Thoughts?

Now the head scratcher - how to design and install a bypass from inlet to exhaust, bypassing the bench for starting.  It's tricky with the inlet and exhaust being two different sizes, not parallel and so close.  I admit I'm reverse engineering here - should have thought this through and designed it ahead of time, but can you see a way to pull it off in the present configuration?  There are off-the-shelf fittings for joining and baffling a 6" and 8" pipe, like these:


https://images.homedepot-static.com/productImages/b46e7009-56ec-42e0-9201-64e7aea39608/svn/master-flow-dampers-ild8-64_145.jpg
But there is not enough room between the pipes to accommodate the fittings.


Satamax suggested in an earlier post that a 4" pipe w/ adjustable baffle would be sufficient.  Could I just cut a 4" hole in each pipe, insert the 4", and mortar around it in?  It will need an operable baffle of course.  

The last photo shows another option, taking an elbow off the top of the inlet to the exhaust, and installing a gate/ baffle somehow.  I feel like this is asking fro trouble - even when the baffle is closed O(which is most of the time) hot gasses are going to rise and mess w/ my draw.

I know that other folks are using split barrel benches, how are they plumbing a bypass into the system?  Any and all ideas most welcome!!

p.s.  These mockup photos use ABS fitting to illustrate, I would use metal, of course.  doh!

OK Mark;  
I've been looking at your set up.
I had to go to your other post to look at more photo's.
The fastest thing , you could put a tee in the vertical pipe. Use the horizontal section to insert burning newspaper.
That is not how I would do it.  

I would remove the horizontal exhaust pipe from the end of the bell.
Cap and cob over that entrance.
Create a new entrance directly thru the top of the bell.
Insert your exhaust pipe about half way or less into the bell. secure it there and cob over.
You may need to lower that pipe if you get to high an exhaust temp or raise it a few inches if its not hot enough.

Max has a lot of experience with batchbox's.
If he says a 4"  bypass is enough then you may be able find a way to connect one up.

Thanks for the reply Thomas!  I fully agree, and in fact just ordered a telescoping stove pipe that will allow me to do just that - it has an outer sleeve that I plan to secure in the cob (still working out how, will post when I figure it out) and an inner pipe that slides up and down.   Should allow me to dial in the right height.  Will need to make sure it doesn't develop leaks after repeated use, and that it doesn't loosen up in the cob over time, but I'm excited about the idea.  Will post when I get it figured out.

I'm still very curious to see other bypass options if folks got em!!

I would put a bypass (4" diameter should be fine) directly between the manifold and the chimney. Use a good blast gate, not just a swiveling damper, for complete shutoff when the system is going well.