IMO, the things that are killin your MPG are:
* the 230 deg cam
* the tq converter
* the 315's wide tires on the rear
* the 750 carb
I would start with the cam. Get something with around 220* at .050, and 112 LS. This may wake up the motor because you will have a compression increase. When you do the cam, also install a 2 piece timing cover (much easier to swap out the cam later on)
Next I would replace that TQ converter to match your new cam. Get something with a low stall. As much as I like that Gear Vendors Unit, I could never pay that much. Maybe one day I'll find a cheap one on ebay.
You will need at least a 31" to 33" rear tire to offset the 4.11's. Just keep it around 11" wide
I would sell that 750 carb and get a rebuilt 625-650 cfm carb. The smaller carb will "work" better with the air velocity increase & the new cam. You can find great used carb deals all day long on line. The good news is that your 750 carb has a good resale factor, so you might make out good on that
The o2 meter kit is a good idea. If you cant afford to get one now, at least order an O2 bung & cap from Summit when you get the cam - like 7 bucks
With the cam & torque converter change, you are looking at around $450.
You can also find a good used vac advance dist on-line (vac advance = MPG)
Not counting the tires, the changes above should give you about 12-13 MPG