Im sorry I call b.s. on this statement. The 72-73 340 didnt make that much less power then the earlier ones. 1 point of compression and a smaller intake valve were the only down grades (actually measured compression of the early cars is less then advertised.) and some will argue the drop in valve size making a difference. Cam stayed the same, Intake and carb was an improvement.
Theres a reason guys run 71 and later cars in stock classes and Ive heard the smaller intake valve is actually a plus in that class.
a 70 318 has probably about the same actual compression as a 72 340, Less cam, worse flowing heads, intake, carb and exhaust so if it is out running any 340 then the 340 has serious issues.