A modern mechanical cam and springs requires what work on the heads?

The 901-16s are a general purpose performanc spring. They'll do alright for a bunch of camshafts, especially under .500 lift. but it's not lift that makes a spring usable. It's pressures and the shape of the lobe plus the rpm potential. The XS274S needs a dual spring, or more pressure than a standard sinlge w/dampener spring. The beehives can have a heavier spring rate and cover more rpm range due to the design. So a single beehive can do more than a single w/dampener and some lighter dual assemblies.
And yes - the beehive needs special retainers and locks - and you'll need the 606-16 set of locks.