What do you need to do to an engine to turbocharge it?

It would depend on the engine..in most cases any car could have a turbo installed

but could it handle it..depending on if it fuel injected,carberated or how high the compression ratio is well most factory tuned turbo vehicles have a compression ratio of 8.0--9.0 to 1 people have went higher but this could damage things... if your compression is high possibly installing 2 head gaskets one on top of another or some places could sell a copper shim to lower the compression (OIL) is needed for a turbo some turbos even come with lines for coolant it could be possible to buy a pump or fabricate a pump to supply the turbo with oil

a intercooler in not needed but is good to have because it puts less stress on the turbo and cools the engine greater also increasing horsepower

a blowoff valve is a must to relieve pressure on the turbo use without one could damage the turbos bearings

a wastegate some turbos come with wastegates this is there to help control boost pressure some turbos require external mounted wastegates