I saw a combonation i have never seen until today. 87 GTA, with the LB9/auto and it had a build date of 12/86.
odd thing was that it has the perimeter valve covers/heads, yet the tpi was all 87 including the divorced coil small cap dist. the engine loked orig as i did not see and fussing with the motor mount bolts along with them haveing slight grime on them. had a digital dash so i dont know milage.

anyone else seen the old style headed engines in factory 1987 model year cars?

 

There is always the possibility of the engine being swapped. You'll know for sure by looking for the last digits of the VIN being stamped on the block.

Anyhow, if it is the original motor, I've seen this before on early production cars getting leftovers from the previous production run. Car production runs usually start in September and end in August (or around there). If the engine manufacturer ends a run later then that, or there was simply left over parts, the cars may have gotten them installed.

Another example is the 700R-4. Hydramatic's production run starts in late June. Thats before GM ends their production run. I have seen late build '87's come from the factory with '88 Model year trannies. I know this for a fact, I'm guessing on the engine theory though.

Of course, the previous owner may have just swapped heads too. I have an '87 and my heads are perimiter bolt as well, and yes, I'm very clean and neat when working under the hood