Hi,
Is there an easy way to see if my -85 Trans Am has the original 305 LG4 engine or if it has been replaced with for example a 350?

 

Look at the block casting number. It is located behind the left cyl head, on top of the bell housing flange. It will be 6, 7 or 8 digits. That will tell you, for certain, what bore size it is, which is the difference between a 305 block and a 350 block. Externally those are the same.

The block will also usually have either "5.0L" or "5.7L" cast in the same area, which refer to the engine size.

You can look up the number at www.mortec.com/castnum.htm

 

on the front of the block passanger side in front of the head on a small ledge near the top left corner of the water pump there should be a stamping with a suffix code following it.. the first few numbers will be the origional vin of the vehicle the engine is from... that may help if it matches your car.. if not look up the suffix code on www.mortec.com.. next place to look is behind the drivers side head on the ledge on the rear of the block by the trans bellhousing. thats the casting number. look that up as well.. if your still not sure pull the heads and measure the bore ....
edit: damn rb beat me 2 it