1987 Chevy Silverado 4 wheel drive

Yes it's possible. Some things you will have to do include: getting different transmission with transfer case for 4x4. You'll need mostly a new front end with a differential for the 4x4 and hubs to lock into 4x4. interior/exterior modifications to put in the four wheel drive engagment stick. Those are the big modifications among other small entities. Doing a project like this can be very costly, yet you can save money on it in many different ways as well. Doing it youself instead of paying someone to do it is probably the biggest money saver. Also, buying used or rebuilt parts can save you money as opposed to buying everything new. So depending on how you plan on going about the conversion from 2 wheel to 4 wheel will determine the outcome of your total cost. Let me know what you plan on doing and I can probably give you a rough estimate.