Carburetors  have been superceded by fuel injection for more than 20 years now, but converting your classic vehicle to fuel injection for most people is still a mysterious process left only to the serious tech heads, but if you have the time to learn a few things about wiring and sensors and tuning chips (EPROMS) you can do it, and open up enormous possibilities!

Here are a few points to consider, in no order, and certianly not a complete overview:

You can use fuel injection systems from other cars.  The wrecking yards are full of great stuff, and most places will make you a package deal if you get a bunch of parts and sensors at once.  Ebay shopping can get the parts too, without making a trip to the yard.You may still need a few other parts, like adapter plates, and an interface module or two, and tuning stuff.

The factory wiring harness will work if you sort it out, but there is a lot of stuff in it that you don't need, like A/c wiring and alternator wiring. if you have the wiring diagram for the car, you can sort out and locate the powers and grounds in a day or two. Sometimes it's best to buy an aftermarket harness or harness kit to save time and frustration.

GM fuel injection systems are well represented on the Internet, there's lots of information available for free, which makes them the most economical to use for conversion.

To control fuel only, GM systems need a distributor reference pulse to determine engine speed. You can get this by using an interface module that filters and modifies the signal from the ignition coil - into a 5 volt pulse the computer can use.  Or, you can convert your distributor to provide a magnetic output that can be fed to a GM ignition unit which provides a trigger for the coil and a 5 volt pulse.  Or you can also use a sensor and a trigger wheel on the crankshaft or camshaft pulley.

Throttle body systems are by far the easiest to install. Multiport is fancier, but takes a lot of modifications to your manifold if a factory multiport manifold isn't available for your engine.

Here Is the most important tip:  unless the fuel injection system you are swapping is tuned to your engine, (i.e. Installing a TBI setup from a 1988 chevy 5.7 v8 on a 1976 chevy 5.7 v8 )  you WILL need to tune the EPROM in the computer to match your engine's fuel flow requirements.  It's like jetting a carburetor, but by computer.

Tuning a chip requires some equipment: for common GM systems, the minimum you need is an EPROM burner, EPROM eraser, some spare EPROM, some freeware from the Internet, a laptop to gather data from the car and a data interface cable or module, and some knowledge. A home mechanic CAN tune a chip.  If you are going to do a few vehicles, there are EPROM emulators and EEprom conversions for your ECU to make the process faster.

Aftermarket engine computers can be programmed without any equipment, but they still need to be programmed, and  most of the same knowledge is required to program any system.

This is just a few points to ponder, when you are considering EFI.  Spend some time surfing the web, there is a lot of good info out there, and some conflicting as well so be aware.   Some searches you can try:  MAF vs MAP  sensor sysems, and VSS.