The only orientation the "T bar" cares about is it's orientation to the points cam or the reluctor. Any change or improper installation, or improper MANUFACTURING between the T bar and the reluctor will change rotor phasing.
The T bar can go on either way, does not matter.
What are you doing about the vacuum? The vacuum advance / advance plate in the dist. DOES change rotor to cap phasing. So if you are eliminating the vacuum, and brazing/ otherwise pinning the advance plate in place, you need to make an effort to position the plate for best phasing
You don't have to have a running engine for this, you can "rig" a piece of hose and drive the dist. with a drill. Take a scrap cap and cut/ drill/ break it so you can see a plug contact, and "rig" up an ignition system. Ground all unused plug towers, and run your "view" tower to a wire and plug for a gap. Hook up your timing light, shine it through the view port, and you can easily see what the rotor phasing is up to.
I have not tried this, but if I were I think I'd investigate a "lean burn" dist. and use your mechanical advance with the lean burn advance plate, which is already fixed.