serial number is also on a freeze plug on the powerhead . . . also check the date on the starter (keep in mind some starters have been replaced). 92 (serial begins with "0D") was the first year of the 2.5L and 91 was the last of the 2.4L. 1988 and later 2.4L should have 1pc heads. Generally speaking the 150's were 2.0L except xr4, xr6, Mariner Magnum II/ III. 2pc top hat style heads (1983 - 1988) 135/150's will have a stamp 3 1/8 and 2.4L will have 3 3/8.
