Couple of questions about my 1973 340.

I have the same motor in my aspen, b&m used to make an external
Balance flex plate for the 904 but it's no longer available. b&m still makes one for the 727, it works on the 904 because it has both sets of torque converter holes but it is physically bigger around and the starter will sometimes hit when engaged. Your starter may clear or You can grind a little off the starter nose or use a newer style like I am off a 94 dodge ram.