Paul,
Very nice drawings indeed.
Clearly shows the problem with a straight in tube, which doesn't go all the
way through.
I did the rounds locally and spoke to all the experts and looked at their
inserts and immediately recognized the potential problem as so clearly shown
in your drawings. I assume that's why the angled insert was used by some.
One could step the port hole and reduce the tube at the end, but adds to the
complexity for the do it yourselfer
Your inside SS insert does address that problem, but I ask myself why not
just use a thin SS insert from the get go!? Maybe your considering the
expansion rate difference - perhaps the silicone potting will address that
perceived problem.
A thinner tube has the advantage of not taking up so much apace, I had a
look at some Titanium pressure tube (1.2mm), actually have some at hand and
thought it would be ideal if I could get some the right diameter - SS would
do the same job this would eliminate the stepped option and would eliminate
the need for two tubes.
George (down under)

I am still looking for some thin wall SS tube.

Probably pretty easy to tig weld over a slotted steel mandrill.
-- 
Paul Lamar ...No rotor no motor.

Paul,
Yes! TIG is definitely the way to go. I have a small Inverter and love
welding SS but as yet haven't mastered the thinner stuff, as I blow holes in
it.
Anyhow, SS tube isn't that expensive, I managed to find a supplier and buy
full lengths - the price isn't prohibitive!
I will ring my supplier and find out how thin the 2' tube can be  obtained
easily off the shelf.
George ( down under)

I have a handle on 1.875 OD .035 wall but I would like .020 wall.
I'll probably use the .035 wall on Marks engine unless some
.020 wall magically appears.