Angled down, oval tips, bottoms cut parallel to quarter panel, exiting slightly behind the rear of the rear wheel well. Dimensions were taken from the original exhaust system, which was still in place. See photo "Exhaust 7" for new tailpipes.
The only difference was that the factory tailpipes had a wide, flared end and that replacement tailpipes did not. Mine were flattened but not flared so do not present quite as wide a side profile.
According to the parts book, the "TA style" splitters were available.
I see no reference at all to rear exit tailpipes for any first gen Firebird.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching