Alright guys here's whatsup:
LT1 w/ 700 r4
LT4 Hot Cam
1.6 Roller tip rockers
Holley 750 vacuum sec.
Hedman Shorties and y-pipe
Test tube
Dynomax catback
No emissions
No a/c
TCC lockup kit

What kind of MPG do you see me getting on the highway?
I was thinking about 18-20 (if I keep my foot out of it )

What do you guys think?

id say about 10-12. my stock 305 doesnt even get past 13 on the highway

You didn't say what gears you are running. Ignition system? Tires? Do you drive on highway a lot or around town? Tuned up good or runs like crap?

But Ghost is most likely in the ball park IMO. I'm sure someone will be along shortly that has experience to prove otherwise, just go with their numbers as I do not have that setup in anything.

Sorry, the gears are 2.73's
HEI w/ accel coil
Tires are 245's on 16's
I'd say 80-90% highway driving
and I will be tuning the crap out of it since im going to try and make it my daily driver until I get my 86 iroc goin

yea mine is my daily driver back and forth everyday to school and it sucks gas up pretty quick..at least in jersey it does and gas is pretty expensive here but use fuel injector cleaner once or twice every month..does save a tiny bit of gas haha

My stock 305 carb when it had 3.73s and it's t5 got like a solid 20ish MPG. And that was shifting at like 2100 rpms MAX and not accelerating like a chi..ummm

But it runs like a champ. Idles low like 550-600 and pulls 20 inches of vacuum. All stock mind you (HO cam).

How good are your tuning skills?

Have you followed Apeiron's extracts from my billions of posts on Holley tuning, up at the top of this forum, yet?

As a very general expectation for combinations similar to yours you could expect around 17 mpg city, and 25 mpg highway, assuming there are no problems and you're not severely out of tune.
It is possible you could see a little less due to your camshaft, or depending on how good your tuning is.
What distributor you run and how you tune it will play a big factor in your results.
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I have to question your entire approach.

Given: "I'd say 80-90% highway driving", why in the world would you put a carb on it? Is there any question that EFI is superior for fuel economy over carb? If you're starting with an LT1 engine, it was designed for EFI. Why downgrade? Nothing else about your combo works better with carb (although a 4L60E would work better than the TH700 if you have EFI).

If your answer is, "I'm more familiar with carb," or, "Carb is cheaper," I'd say you need to get over it and recognize the superior flexibility of EFI (and converting an LT1 to carb is hardly "cheaper" than staying with EFI). If you had said "80-90% drag strip use", I might be able to forgive the choice of carb - but even then, the LT4 Hot Cam is pretty mild for a track-primary car.

Well with you completely, I bought the LT1 with the intent of using the EFI. But what I want and what I need are two different things. The engine in my car at the moment is on its last leg and since it is my daily driver and only means of transportation at the moment I need to have it running, even if it means putting a carb on the LT1 and throwing it in for 3-4 months.

I had previously bought another LT1 with the carb intake and all that jazz for cheap and had it laying around for another project that didn't happen. I dont currently have the funds or the time to get the harness finished or the computer tuned, or the rest of it for the EFI. My father is giving me a Holley 750 to throw on it for now and I was just planning on putting it all in my car for now until I get the funds/time to get the EFI going. To get the carb on the motor and running all I need is a regulator and a rebuild kit for the Holley.

The idea from the beginning was to have a nice daily driver that had some power behind it. It's not a primarily race car so I plan on putting the EFI in it as soon as possible. I just need to get the motor in it for right now. It's not that I can't come up with the funds eventually but I have them tied up in items that need to be sold first so this is just a short term ordeal. (Too many projects at the moment). SO Five7 I completely agree with you and want the EFI in it eventually, but I just need a running car right now.

With a similar setup I usually get 14-17mpg.

If I could get the 600 carb dialed in better it would probably get better. I would definately run EFI if I could.

My thirdgen gets 13ish on the freeway doing 60-70, that's with a th350.

In that case I'd say sell the LT1's and build a Gen I for carb. I think you're kidding yourself about what it'll cost you to get the LT1 running with carb.