I have a 1968 350 in my 1969 Bird. When I bought it it was a 2bbl with #17 heads, an ST300 two speed automatic and 2.79:1 gears. Needless to say, it was a pig.

I put a Quadrajet on it first, and the improvement was worth the effort, but not all that dramatic. It sure sounded better when the secondaries opened up.

Next, I replaced the 2 speed with a TH350 with a shift kit. The lower first gear and closer gear spacing between the 3 gears made a huge difference in driveability. The throttle response was better everywhere just because it seemed to be in the right gear all the time.

Then I upgraded to #16 heads and an aftermarket cam with the following specs: lift .420/.443
duration @.050 204/214 (270/280 adv)
overlap 51 degrees

I love the performance now. There's no way it's 350 hp but it's lots of fun. Pontiac advertised 325 hp for their 350 HO in '69. Mine would need 3.55:1 gears to perform like a 350 HO, but trust me it's nothing like the pig it was. Now the rear tires break loose often enough to remind the neighbors that I have maturity issues.

Go as far as you want but be careful with recommendations for too much cam, carburetor, or anything else out of balance.