my 86 was not tpi. i'd like to hook up an external fuel pump and regulator for the LT1 swap. what are the pros/cons of this setup and does anyone have it?

Pros - easy to install, no needing to drop the tank.

Cons - loud and can overheat causing vapor lock

intank

Pros - quiet and keeps cool by the fuel

cons - have to drop the tank, which can be an all day job

If you can get a TPI setup for the fuel tank(or the complete LT1 fuel tank, it will bolt right up) you will probably be more happy from not having to worry about the fuel pump overheating or the noise from it when it is running.

the tank from the LT1 car was damaged because of the car was in an accident. Will the Lt1 fuel pump fit in the third gen gas tank?

nevermind. want to go with a new pump

here's the new problem. maybe.

The 86 4-brl didnt have the fuel pump in the gas tank. Is there anything else i need besides the in-tank fuel pump to make the old gas tank setup work with an in-tank fuel pump?

If you can find the framework which has the sending unit and all the hoses that go into the tank from either a F-body V6 MPFI or TPI car either will work since you're going to put a new pump in.

One thing to keep in mind is that you will need to make a flare fitting on your current supply for your new setup. Because you originally had a carb, you probably have just a rubber hose with clamps on either end. While this is fine for the lower PSI of a carb setup, it will not do at all for a fuel injected system as they run much higher pressure. The last thing you want leaking is fuel. You can either find a new sending unit from a donor car with fuel injection and flare the original supply line on the car while having a rubber hose made or run your own new line up to the front. Either way, you'll need an injected sending unit.