magnum or pre-magnum that is the ?

Why are you looking to change water pump and flex plates????? If you are converting an LA all you are switching is the heads and intake,taking the 273 hasn't been in production for a while, just check for the oiling ov the valve train. It should be balanced as an LA, flex plate should stay the same as well as water pump. Look at the crate engines. They are the same architecture as an LA engine just has the magnum specific parts. Now, Yes, PRODUCTION Magnums that are in the trucks do have a different timing chain cover and water pump. If any one wants, email me and I will give you the name and number of the guy who I talked to, he is a Performance Specialist at a Dodge dealer or call Mopar Performance personally and I can scan my article from Mopar Muscle, who converted an LA engine, and email it to ya'll!!! :salut: