you are to funny...post #15 says my tire burning days are done (like mine)....and now you want to burn rubber....AND chirp the hides on a shift!
1974 L82 is to far back for me to recall details but it was only a 8.5CR? 250HP motor same as the 8.5CR=150psi 250HP you have now....
if you were chirping the hides with 3.08 gears it was very like due to "ALL the parts "tuned" and designed to work together" for peak performance as F-bird posted
On the 74' vette, the tranny shift vacuum and rpm's modulator valves rpm's shift points were tuned to the cam shaft (which was a WOT "mid range power" 222/222 cam) and dist curved to work with that camshaft and CR (correct spark timing can be 30HP gained over the whole rpm's range) ....
crummy mpg and a dog can be from many things (read your plugs) but
'fair chance" your tranny does need some attention...maybe just the bands adjusted for better shifts or a correct $15 vac modulator tuned to the rv cam...tranny's do need a tune up....(I do not believe in "a fix in a can" at all but I've have seen good improvements in shift quality with the $9 Lucas Tranny conditioner/cleaner many times)
can you tune the tranny and motor to chirp the tires with truck heads/2.73 gears/rv cam/and tall(?) tires.....IF this car does weigh about 300-400lbs+ less than the vette did....probably-maybe-yes with maybe a shift kit also needed
re: gear swaps
this is the best (basics) article I've found for explaining all about gears
you can buy a "brand new" GM complete 250HP long block for $1500 (which will also comp test at 8.5CR= 150-160psi!!!!) ....basic re-machine a block and heads is about $1300 around here (454 left out balancing and cleaning) plus $300 for the parts...assembled and tested is $1800/3 year warentee....you can buy a 290HP (on open tube headers) brand new GM long block for $2000 for a better chance of "chirping" the hides (270hp with exhaust pipes)
just mount your vac guage on the dash so you can read it while driving to know how hard the motor is actually working.... and re-train you right foot to keep it above about 12Hg accelerating.... and tune the motor for max Hg at hwy cruise speed will gain you atleast 2-3mpg+ combo intown/hwy
I'm guessing that your car weigh's 3,000lbs...with the rv cam the guage should be reading 18Hg+ at 60mph on a level road (really tweeked it may read 20Hg)
hard to read in the pic' attached but it does say "poor gas mileage" in the yellow/brown band below the "best economy" green band"
Hg reads low=carb is rich
hg read high=carb is lean
edit: LOL...thought about it...can the rv cam "chirp" the tires???....kinda depends on how much weight is in the rear and no posi allowed....might only be a "cheeeeep" on a "open rear"....which is likely what you had on the vette to chirp them
ps: which model Edelbrock did you buy