How do I know what distributor I have, in my 1989 Trans Am w/ 305tpi.

 

If its all factory it'll have the est type. The 89 has the small cap with the coil separate of the dist, the electronic hei has a big cap with the coil on top and a 4 wire plug on the passenger side of the body, a vac advance hei looks just like the electric hei only it has a vacuum pot where the 4 wire connecter is on the electronic hei.

 

All are versions of the GM HEI (High Energy Ignition) Dist;
the electronic version used for EFI engines ( the only type you can use with a factory computer ) is known as a computer controlled HEI;
hence the 4 wire plug underneath that connects to the ECM and EST.