try to use brackets, accessories and pulleys all from the same year engine. Buick varied the depth of the water pump snout, so if everything is not working with that and the crank pulley it might be hard to get it aligned.
Buick 350 production ran to 1981
BUT
the Buick v6 is the same architecture, just two cylinders less. they are also a possible source for pulleys / timing cover / etc. there are even serpentine options available from the mid-80s or so
this would be the 231ci v6 even fire, the 3.8L 1st gen and the 4.1L. production on the 3.8L continues to at least 1989 in the Pontiac Turbo Trans Am.