Could I just switch a LG4 carb for a H.O. carb without redoing anything else or do I have to mess with the ECU or anything else?

By H.O. you mean L69? They're essentially the same.

Oh are they so I don't need to change anything then right? (I am considering buying a L69/H.O. for my Camaro)

Any differences between them are fairly minor.

Install a set of DR seconday rods on a J hanger and PRESTO! You have an L69 carb. There are no other differences that I'm aware of.

Oh I don't actually have an LG4 in my Camaro. It has a 350 with an LG4 carb.

... so lets clear everything up, your running a stock LG4 carb on a 350 w/the LG4 ECM controlling spark advance?

Haha. Wow, if you are then you are limiting that 350 BIG TIME.

Yes I am. Some previous owner dropped a late 60s-early 70s truck motor in it.

How all of the aftermarket carbs are rated at 600CFM and from what I have read the stock Q-Jet gets 600CFM stock and you can get it to do 700CFM.

Then you need better rods w/hanger, and an L69 prom (has a much better spark curve)...

Not so much.

NOT AT ALL...The 70s smog heads and tiny stock cam are choking that 350. If it still has the LG4 exhaust its even choking it worse.

So new exhuast, heads and cam will really breath some new life into it?

Yes

Ok, my bad. Whenever I think of someone dropping a 350 in. I don't assume it's a stock 350 with smogger heads. To me that wouldn't even be worth the time.

Even if it wasn't a smogger, a Qjet will happily feed just about anything you'd want to run on the street.

Well, I am not going to get into that argument.

I know I am not the one that put it there, but even if it had nice heads the Q-jet would still feed it just fine.

FYI, my 400hp 12 second 350 LG4 (was a 305 obviously) is not being limited by the carb, but by the heads and cam. So anyone who tells you it is a limiter until at least 450hp is blowing smoke up your buttski. Assuming the carb is working correctly.

The carb is going to be rebuilt