I have a 87 firebird trying to figure out what engine is in it to see if it was ever swapped I found some numbers on the block behind the alternator but still can't find out what they mean hoping a knowledgeable person might know

 

The larger #s are the stamping code for the specific engine, as it was installed into a vehicle. Would trace back to what induction system was on it, what accessory drive system, what exhaust, and so on. The last 3 letters are the easiest way to look it up.

The smaller #s are the last few digits of the VIN of the vehicle it was installed in. If they match yours, it's your original one. Looks to me like they don't; if original, it should have a "L" where the "H" is. L was the Van Nuys assembly plant, which was where all 87 Firebirds were built; I don't know what plant H is. Although, some of those look like they've been tampered with: those last 2 don't look the least bit like factory 5 stampings.

Bear in mind, even AT BEST, those #s only tell you about THE BLOCK. If somebody swapped heads, cam, pistons, or WHATEVER else, then THE ENGINE won't be the same one that the numbers on THE BLOCK say it once was. In virtually ALL instances, particularly with swapped motors, this applies. Virtually NO ONE EVER takes an intact small block Chevy out of one vehicle and drops it unaltered in any way into another. So, even if you find out what THE BLOCK came in when it was new, that probably won't tell you A DAMN THING about THE ENGINE as it sits now.

Better to look at the block casting #, conveniently located in the most conspicuous location possible: on top of the bell housing flange behind the driver's side head. Similarly, look at the head casting #s, which are under the valve covers in between the rockers.

 

https://www.thirdgen.org/forums/tech...tion-help.html

 

The suffix code SDB indicates a 1987 LG4.

 

And the 2HL212455 should match your VIN.

 

SDB 1987 305 150 4 Roch E4ME carb.