Can I convert a carburetor 454 motor to fuel injection on my 1979 chevrolet 3/4 ton puckup which has a 1991 rebuilt engine?
No.
With all of the modifications needed it would be easier to turn it into an electric vehicle. Easier yet to get a good deal on a new one at this point.
Yes, Holly makes a bolt-on conversion kit to a nice throttlebody unit. You could also use a factory throttle-body set-up if you could find all the bits and pieces.