Bad idea. If your truck was an 88-94 I'd say go for it, but not 96+.
I put a TBI 5.7 in a 94 and drove it for 16 years. Wish rust hadn't killed it.
You'll be money and time ahead if you sell the TBI and buy a 96-02 Vortec 350. Your wiring will be greatly simplified (just 4 additional wires) and the fuel system is ready to go as is. You also gain 60 or more HP over TBI w/o changing the fuel mileage or driveability. Assuming you currently have a 4.3.
If the truck currently has a 2.2 you'll need to find a 96 4.3 to steal the complete engine harness and fuel system off of. You'll also need the transmission since a 2.2 trans won't bolt to a 4.3, 5.0, or 5.7. You will more than double the HP at the cost of some fuel mileage.
Around here good TBI 5.7's are selling for as much as, if not more than, a good Vortec 5.7 because they are starting to get scarce. So it should not cost more for the later engine.
Making the TBI system work on a 96 up would be doing things the hard way to end up with less power at a greater cost and degree of difficulty.
BTW swapping in an older engine is a violation of Federal Law which carries a $2500 fine.
If your state has emission inspections the TBI will flunk while the Vortec will pass OK.
Not to mention being bad for air quality.
Even is you got the TBI free, putting an L31 Vortec in will cost less in the end.
These comments are based on actual experience from having done the swaps. I currently have a 98 ZR2 with an L31 Vortec in it.