[hatzie]

You're going from the 250 Inline-6 to a 5.7L V8.

The 97 Vortec motors probably do not have the mechanical fuel pump boss machined, or the fuel pump cam eccentric, and definitely don't have the push rod for a mechanical fuel pump.
You'll need an electric fuel pump that provides 6PSI for the carburetor or a bypass-to-return-line regulator.
If you run a frame mount pump it needs to be able dry lift prime without damage so you'll have to do some research to find one.
The easiest thing to do is run the 1987 TBI tank(s), Delphi in-tank pump(s), and modified 1987 fuel pump wiring. You'll need a 6PSI bypass-to-return-line regulator. If you'll eventually be moving to an LS this is a good time to update to the baffled fuel tanks to make that transition a little easier.

The 250 bellhousing will bolt right up.

You can't use the 250 clutch parts on a 5.7L V8. The flywheel is the wrong balance and probably the wrong bolt pattern. You'll need a flywheel for a 1987 and later 5.7L with a one-piece rear main. GM changed it in 1986 but it's rumored there are some one piece and some two piece rear main engines scattered through the 1986 model year. 1987 is a safe bet. I'd stick with good names in the clutch game. Sachs, LUK, and Valeo

The 1987 & 1981 350 pressure plates are the same. I'd just get an LUK, Sachs, or Valeo 1981 350 smallblock clutch kit. The pressure plates are the same but the Hydraulic and Mechanical linkage throwout bearings are different. Complete kits usually have a plastic alignment tool included with the disc, bearing, and pressure plate.

V8 clutches can be had in 11" & 12-5/8". Bigger is usually better. The flywheel has to be drilled and tapped for the clutch disc & pressure plate you want to use so pay close attention to what you order.
You'll definitely want to bolt the flywheel to the engine, install the clutch, install the bellhousing, and turn the crankshaft to be sure there's no interference before you install the engine so you aren't working in an inconvenient position.