it depends?
the heads will interchange between the them, so i guess pick the better of the two pairs. the cam is a no-go, roller doesn't go into the early block without a fair amount of fussing and fighting. i'd just pop for a new hydro or solid unless you absolutely have to have a roller, in which case open up your wallet for a retro fit. adjustable rockers are same/same.
personally i'd leave the 72 bottom end well enough alone. snap the heads on, stab in a cam and ship it.
if you're looking to swap that 73 340 crank into the 72 motor, that's a whole different game plan. it can be done but there's considerations, namely among them balancing the rotating assembly.
what's wrong with the roller block in that it is "not able to run"?
