i don't know about all the work and money these guys want you to spend.
I see it has 14" tires and probably 3.23 gears.With that i would suggest leaving the cam alone.I have driven a few stock 14" tire 340 A bodies and if well tuned they pull very hard on the street.
Maybe that thermoquad isn't working right and may have vacuum leaks.I'd start by recurving your distributor and putting on a new 600 carb.
Perhaps replace the three speed with a 4 speed and tune...tune...tune.
That car should run hard on the street and take no prisoners street light to street light