If the l2 is a hydro, it has the big engine. If it's a belt drive, then it could have either. Check the model n plate on the engine. 3500 is the 426 (big engine). I believe the small engine is a Mod.n 2600IJ Ed in Montana
The engine ID plate is on the left side of the motor and is accessible through the grain tank door or by using a mirror. It will identify the engine as one of three available. In 1980, AC listed three engines for an l-2. Standard was a 649T, a turbocharged 301 CID diesel @ 130 hp. Options were a 649I, same engine intercooled for 145 hp. The big engine was the 670T, a turbocharged 426 CID diesel rated at 158 hp.
Its a 1978 with hydro and I had heard if it had hydro it had the big engine, but I had also heard they could have either. Also someone told me I could tell by the exhaust manifold. So thats why I came here because it seems you guys know your combines. I have had this for 2 years and still haven't got a positive answer. Thanks everyone.
I should clarify that when i said left front of the engine, it is as if it were in a tractor. The manifold is different, but probably the easiest way to tell is that if you have to pull the grain tank access door to change oil filters, it is the small engine (649 I or T) if you can change them from the back side of the engine compartment it is a big engine, (670T).