there are differences
a/c or not matters
is the biggest difference
the manifolds changed in 81 on light duty sbc engines to a new design above the spark plug like on the cars
and the 70s ones were old style below plugs
the brackets there were slightly different ones
some used a threaded stud on the small tirangle adjuster bracket that bolted to the exhaust bolt and some used a bolt with slot in it.
if its for a 73-up truck then you can make it work with minor shimming with washers etc
if you have all the matching same brackets
and all '73-up long water pump style pullies on the engine
(the cars changed to long pump in 69)
there was also the van style ones which were the most simplest they bolted down low on face of the engine block those two threaded holes in it and used the same cast iron cradle bracket as the 72 older trucks, just was a carried over old bracket for the vans 73-up. the steel flat bracket reached up to first exh manifold bolt
very simple and works on long water pump engines.