My personal opinion is that the original engine was replaced with an engine from a junkyard 455 from an early production Riviera (H18 intake is August 18, 1969 , not 1970. This matches the carb date code as well. The transmission came from the same Riv and was in all likelyhood, changed to a short tailshaft version when installed in this car. People change tailshafts all the time to get what they need for their application. It is highly unlikely this is a "factory swap" given the great differences in date codes of the engine, carb, trans, etc. and the car itself. Somebody blew up the engine and swapped in a complete unit from another car including the trans after changing the trans over to a short tailshaft version.
Brad you are right about the date being 69 but how do you account for a BA tag being on the main body of the trans. Also if you blew the engine why change to a long tail when you already have a short tail.
The mystery is finally solved and the answer is......... I am a dummy, I thought the trans tag had the trans vin on it, it turns out by coincidence that 3 numbers i read on the trans tag matched the vin on the motor so I thought they matched, but through further research i found the location of the trans vin and it does match the car not the motor, so it has the original transmission but not the original motor. Thanks to everyone for your help.
Now that makes sense. Motor blew and was replaced with Riv motor from junkyard. Trans was OK and still matches car.
