new to me 68 Barracuda Conv, sluggish 318

you just bought a carwith a bad combination of parts 340 heads with low compression 318 pistons yeah it will be a skug . How does it feel once you are past 3500 rpm ? good news is you got a nice car that with a few simple repairs / work can be a screamer .
I'm sure AJ ha a thesis paper on how to get you going . lots of good people with loads of info here to get you on the right track