More details about the actual cam would help , but it looks like it has lots of overlap / low idle vacuum & is probably the main culprit .
Any idea what compression ratio the engine has ? I would run a compression test . if the numbers are low you may be wasting fuel with not enough heat / pressure especially with alum heads the cam can also affect this with long duration bleed off pressure , also were the heads port matched , these are notorious for horrible core shift , a friend of mine worked at a speed shop & went through 10 sets when they first came in & bought the best 2 heads & showed me how badly cast they are.
The carb is oversized ,,, I almost never say that , ideally 2x the CI is right so around 700 cfm but this is not the cause of bad fuel mileage especially with vacuum secondary as the engine will only use what it can draw in , QF is a great carb & tuned well should give great fuel mileage so that is the last part I would replace in your combo .
Tuning will get you a long way so start there , you want timing set to 16* @ idle with 36* @ 3000 rpm . take your engine vacuum at idle in gear , probably in the 8-10" range , make sure you have approx 4.5 " power valve . how do the plugs look , tuning with an O2 is far more accurate , you could be over jetted & wasting fuel .
Awesome car BTW
