I measured the exhaust mounts and they are 1 1/2 " on center and a quick glance at the overall exhaust is about 2" so with that and the 49zn2 i'm going with it must be a 4.2. Now I did read something that if the crank case was milled it had something to do with ???just cant remember what? The crank case is milled. With that said do I need to open it up and check the crank as you guys mentioned? Second the engine has only had about 3/4 of a gallon of fuel ran thru it for break in according to the original owner so what is the expectant crank failure if it has the older crank? One last question is what type of ignition module should I get for it? I will call the above mentioned company this week but was looking for recomendations. Thanks sorry to be so long winded... .