Motors were built a couple of weeks befor going to the car asslembly plant to be installed. Asslembled cars did not sit around waiting for engines to be built. If your car was built on March 16 it had a engine in it at that time. A March 20 engine could not have been factory installed.
I am by no means an expert on production times. Don't claim to be. I would agree that most engines are built prior to the body/chasis time. However, there are too many examples of hold overs, special orders, and like mine, strikes at certain plants ( 1965 ) that could easily explain the 4 day difference between the motor and the car. Remember, cars use to be able to be ordered from the dealer, not just purchased what was on the lot, many were in fact ordered to customer specs not GM'S production line. Now I am not saying anything is right or wrong here. I just think that if the block is stamped with the VIN, chances are there is an explaination for it and it is most likely genuine. That being said, lets look further without predijudice. Like I tell everyone. I cannot PROVE ( Yet ) my 65 impala is a factory 409 car, however there is no-one yet that can PROVE it is not. It has everything the car should have per everything a 65 409 impala should have, however I have not done a title search for the original owner or second, and chevrolet doesn't keep records like Pontiac did, so who is to say? I am researching it though. Even with my car as a cover car for Super Chevy listed as a 409 impala, I still need more. Too many one offs, special orders, plant strikes, delays, clerical mix ups etc., to know for sure. And the dates are so close. Someone really wanted to fake that car if its not real, and what would be the advantage? It's not that special to fake? So why would they?
Yes the car was ordered by the customer. I am the second owner and it has sat in a shed since 78. By no means do i think its rare but it does have some interesting features such as two tone paint black top and glacier grey body that is noted on the build sheet. I had heard that two tones were unusual on the 65 super sports.
Only thing I can think of is maybe the engine was stamped wrong, or could be a factory replacement engine, replaced under warranty and stamped at the dealership. I do know that your car was built with a engine installed in it on the assembly line and could not have been built with a engine assembled later. Engines and cars were not built at the same plant. Engines were built and stamped , then shipped to the car assembly plant to be installed when the car is built, not after.
Upon closer inspection of the sheet i realized the 03-16-65 is under the box marked schedule no. and date and not under the box for date produced which is unfortunately blank along with everything else on the top line except a handwritten body no. of BA 10071 and the vehicle ident no of 1663750. I dont know how this date corresponds with actual production date. Also not marked on the top of the sheet is the eng or motor unit no.
I understand the engine was built in a different location and i am sure it took at least a few days for shipping to the assembly plant. As far as the stamping on the engine i am guessing the date and location of engine build is stamped on the rt side of the pad and then stampef with vin on the left side at assembly plant right? Perhaps on the engine date stamping was supposed to be 0302 instead of 0320.i dont believe the engine was swapped out. However it does have some interesting cables tieing down the motor to the mounts on each side. I think that may have been a recall. I also had wondered what the type 96 was behind the L35 on the build sheet.i cant seem to find anything pertaining to a gype 96 in any of my research. I understand the point of cars not coming off the line without an dngine but maybe it was close to the transiition time from the 409 to the 396 that since it was ordered that they were waiting on a shipment of 396 engines. It sure has a set of early casting heads dating 12 22 64 i thought that waz pretty cool.
After giving this some thought this is all pretty much common sense. The motor build was march 20 the build sheet was for the BODY of march 16. Both were built and shipped to doraville prob arriving bout the same time. Mystery solved