new to me 68 Barracuda Conv, sluggish 318
This.
And elevation.
140 is where Performance starts
150 is Running pretty good
160 is As good as it gets with iron heads,
130/140 is typical at sealevel
120 and less is super soft
A big-port intake will only exaggerate the problem.
The usual way to bandaid a soft bottom due to low-cylinder pressure is; with plenty of stall, mid to high 3-series gears, and a fantastic tune. A small 4bbl on a smallport/small plenum, helps. Ideally you would need to increase the compression ratio to work with those heads. Been there/done that.