Hawks62, I just recently went through the same thing with my L6...trying to determine a) if it was original and b) what the cube was. There are very few visible differences between the 230 and 250. This might vary per a given year, but for example in 1966, the stroke on a 230 is 3.25 and on a 250 it is 3.53 (Source MOTOR Manual 1967). You might try the suffix code, which is a two or three letter code that trails the engine serial number stamped into a pad just aft of the distributor. There are a couple of websites you can Google for suffix codes. Most of them are V-8 only, but I remember finding one or two sites that had L6 suffix codes. Here is one example: http://www.chevellestuff.com/69velle/69engine.htm