i have just pulled a 350 vortec out of a silverado and im trying to drop into a 74 impala but this will be my first time dropping a motor in an im trying to see what all do i have to do to change the fuel injected motor into a caurberated motor  

depending on the year you may need to make some minor changes,the big one will be to get a carb manifold to fit the vortec heads. no big deal. open up summit or jegs.youd probably want to pick up an HEI with vac advance from a mid 70s chevy small block or put up the money for an aftermarket one. im not positive, but the cams may not have  a lobe for a mech fuel pump because they obviously didnt need it.

you could also check out painless wiring for a standalone harness and computer to keep that vortec the way it is. its not the best EFI but it would run smooth and get decent mileage is tuned and maintained.  

Also remember that if you are swapping in another cam it can't have over a .470" lift or you will have to have the heads machined.