My sig car was bone stock except for MP electronic ignition when I bought it in 1981, and it got waaaaay better than 10 on the highway, around 14+. I drove it to Myrtle Beach from Virginia in 1982 and I remember it wasn't terrible.

My compression ratio was advertised as being higher that yours, although I didn't measure how far down the pistons were in the hole when I built the motor the first time in 1984. Ah, the indescretions of youth!

You've got some good suggestions so far. I assume you have a stock cam since you're running the stock AFB? Those carbs were calibrated very well for the stock engine, and should give razor-sharp performance and decent mileage if everything is as it should be. You might want to get an O2 bung welded into your exhaust somewhere and pay someone with a wideband meter to give it a look-see to be sure the factory calibration is still intact. Someone may have changed jets, metering rods, springs, etc. I still have my original AFB disassembled in a box - if necessary I can tell you which rods and jets it has. Springs might be more difficult to identify.

With a dialback timing light or with a timing tape installed, be sure the advance curve looks good, and be sure the vacuum advance is working right. The spring tension on the vacuum advance is adjustable if you're running a stock distributor or the MP unit - if you don't know how to adjust it one of us will explain it if you're interested.