I am very sorry if this has been posted but I was not going to go through all the posts looking for the answer.
I am in the process of swapping engines and we decided since the L69 was destroyed internally we got an LG4 for free. We are putting all the L69's external components on the LG4. While doing this I noticed that the L69's carb had a different model number than the LG4's. Naturally in search of xtra horses i put the L69's carb on the LG4. But I am wondering whats the true difference between the LG4 carb vs the L69 carb. And if there is a HP increase how much is it?

 

Possibly different main jets, typically different secondary rods, and sometimes the LG4 secondary air valve is limited to how much it will open.

The L69 is the slightly better carb as-delivered, but nothing that an LG4 carb can't be made to do.

The big differences were with air cleaner, cam, and exhaust. Another slight difference was the PROM tuning, but if you are keeping the L69 ECM, no problem.

 

You mean the computer inside the car then yes if you mean something else let me know so i make sure it makes it on.
also we are keeping the exhaust, ram air setup, air cleaner, in short everything is L69 in terms of accessories and stuff like that but the cam unfortunetly didn't make it. So we are forced to keep the LG4 cam. My dad blew up the L69 five years ago and the deal was we make it go again for cheap and If i do the work the car's mine. The LG4 is a 87 and the ports are a little bigger but still match up.

 

There were also some vacuum port differences on the carb between '84 & '87 which drove the # difference, but since you're using the '84 carb with the '84 equipment, no problem.

Yes, I meant the computer inside the car, which I figured you wouldn't be touching.

The LG4 cam will be a bit of a downer, but the '87 engine has a roller lifter cam, which is a slight upgrade. A replacement cam for it will be in the $250 range. But, you can reuse the lifters. The '87 engine also has a slightly different intake manifold and heads, in that the center two intake mount bolts on each side are at 72 degrees instead of 90 degrees like the rest.

The rear main seal type changed in the 1986 model year, so your '84 flywheel won't fit the '87 engine. Most likely the '87 was an automatic, so you're going to have to find a flywheel for the '86-up application.

Overall, it isn't a bad swap, just a very slight downgrade power-wise due to the slightly less aggressive cam. Hopefully, you still have the L69 air cleaner.

 

How funny. I ran into every one of those problems. we found a flywheel but we also have to replace the clutch as well. yes i still have the L69 air cleaner. As for replacing the cam I think the cam is ok but my bro decided to use the rest of the block with the cam still in it as a counterweight for a trebuchet. and he painted it to keep it from rusting bad. since we already have it ready to go in and everything with the exception of the clutch and the fact that we didn't have the money to get a new cam we decided to leave it alone for now. But I found out I could get a rebuilt L69 for round 1200 bucks so I am going to go for that. The other way i was thinking was a 383 stroker but all i am going to do with that is smoke the tires to kingdom come. The goal of this was for me to practice as I am a Auto Restoration Major and to get the car on the road before it falls apart.

I looked it up and the exhaust system was 1 and 3/4 inches out of the one we took it out of and it made 165 in the donor caprice that it came out of YES ITS THE SAME LG4 because i looked it up. well the L69 had an exhaust system that was a half inch bigger.