is there really no replacement for displacement?...
I purchased my 68 Barracuda in 97 and worked on it to mid 00 when I put it back on the road.
It went on the road with the original \6 and an A833OD 4spd tranny and 3.23 gears. I drove it that way (making other changes along the way) until Jul 05 when I swapped in a 360 with the same A833OD and 3.55 gears. I figure the \6 built the way I had it was making around 190 HP and got 19-20 mpg around town and 22-23 on the hiway. The 360 is making around 370 HP and gets 16.5-17.5 mpg around town and 21-22 mpg on the hiway.
I drive the car between 7k and 9k miles per year and have not regretted swapping in the 360 for a second. Yes a \6 with headers and a 4bbl looks cool but it doesn't really perform like a muscle car and it doesn't sound cool when talking to someone about the car, all they hear is \6. The 360 on the other hand is fast and doesn't really give up much in the way of economy and i don't have to make excuses for having a 6 cylinder.
This is the way the car looked with the \6;
And this is the way it looks with the 360;
I don't think you could get the \6 to the 370 HP and 400+ ft-lb range for the same cost as building a 360 and installing it.