Prelude Si engine

If there are any honda engine experts in here (which is prob a dum thing to say) PLEASE clear up something for me. What size engine is implied by the letters "Si" in reference to a 91 Prelude AT? My mechanic (currently trying to rebuild my engine which is not the original) ran the VIN and said that it came back supposed to be a 2.2, but when the head gasket didn't fit, he was told that some were made with a 2.1. Well, that didn't fit either. After extensive research several weeks ago, I came across many times that my engine was a 2.0[5]. The guy I bought the car from (son's old car, they had to have the orig engine replaced) tried to say that the Si's came with 2.0 engines. Which it the right size? and what would the JDM # be?:confused:

Well...there's a "2.0 Si" and an "Si". The 2.0 Si obviously came with a 2L engine, and the Si came with a 2.1L engine. But if it was replaced, then none of that may even matter at all. You should look for the engine code on the front of the block. It's a flat plate where the engine meets the transmission. Like here:
http://img.photobucket.com/albums/v473/CivicSpoon/plate.jpg
This one is a '92-'96 JDM H22A Prelude engine. If it was a USDM engine, there would be a number after the A (like H22A1). And the first 2 numbers in the engine code represent the displacement. So with the H22A, it's a 2.2L. The B20A5, from the 2.0 Si, is a 2.0L. And the B21A1, from the other Si, is a 2.1L. I honestly have no clue what the JDM counterpart for the '91 Prelude is.