T Bar in Distributor

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.