I recently acquired an '87 Stumpjumper and am considering upgrading from the friction shifters to indexed shifters. Can anyone give me a rough idea how complicated and how expensive this might be? I want to know if it's a possible DIY for me since I kind of bought the bike as a project bike and would like to learn more about bicycle mechanics.
At the highest level. a new freewheel, rear derailleur, shifter and cable/housing will get you rear indexing.
The freeqwheels with the advent of indexing have specially shaped teeth to assist the shifting (either twisted or ramped).
The manufacturer of the derailleur should match the shiftershould match the freewheel (although some compatability across manufacturers exist, the easiest thing to do is keep them the same). The number of "speeds" should match between the shifter and the freewheel, the derailleur doesn't usually matter.
If you choose to replace the rear wheel for a freehub/cassette, then substitute the term cassette for freewheel in the above. Freewheel is assumed for friction shifting system, since I don't recall anyone mentioning any friction shifting cassette systems.
Indexing on the front is the same without the need for a freewheel change... although updating to chainrings with ramps and pins can help improve shifting performance.
Are you hoping to increase the number of gears as well?
How many gears do you have now? How many do you hope to have?