i need some engine advice

Check your balancer and engine #s !!

They started putting cast cranks in 340s on April 11, 1972.

Starting with engine # HM340R-3911-8000.

http://www.hamtramck-historical.com/images/TSBs/1972/09-07A-72C page_1.jpg

http://www.hamtramck-historical.com/images/TSBs/1972/09-07A-72C page_2.jpg