GA16DE or SR20

hi guys...I have a Nisasn sentra 95, but the thing is that my dad replaced the engine for a 97'. I would like to know if there is a visual diference between the engines GA16DE and SR20. I talked to fugiot a week ago about changing the Pulleys. I looked at the pulley for the crankshaft and it only supports one belt. The SR20 has two slots for two belts. Now....I was taking look at my car and the crankshaft pulley has two slots... So I would like to know if the engine is 2.0L or 1.6L....It is 16 Valves and has some numbers with a yellow color, but I can't find SR20 or GA16DE...Thank you
Sorry if that's a dumb question..,..Is there a difference between SR20 and GA16DE visually

try looking for an engine code around the transmission/block junction

GA16
http://www.ctjengines.com/nss-folder/pictures/Ga16de.jpg

SR20
http://www.adelaidejap.com.au/images/Sr20.gif

basically the easiest way is the sr spark plug wires are down further in the valve cover