71 Duster Dyno

http://www.hughesengines.com/TechArticles/11360dynotestfeb2000.php
Go to Hughes dyno build-up #11

From your pics, you are running the rear pretty low. Is that cuz the springs are soft, or cuz you like it that way?From the dyno video, the rear looks pretty soft.When you lifted at the end, the back did a little dance. I'm betting the pinion angle is going from waaay wrapped up to waaay pointing down, and hauling the shocks around wherever it goes.
Sway would be chassis; be it springs,shocks,air-pressure,or steering components. Could also be air getting under the front, or a heavy crosswind.New springs with a little rake in the back, will help keep the wind from getting under the front, while planting the rear.Perhaps the shocks will be able to control things better then, and reduce the sway, to an acceptable level. If not, new shocks, perhaps all 'round, will do it.(barring steering issues)

From your mph, that engine is sleeping. Either you are short shifting, or your rear gear is way off, or she's lazy. With those skinny tires, that 360 should be spinning to 60/70 plus mph.
If you're in 4th@150,Ima guessing you're running 3.91s/4.10s; or you are short shifting a much smaller gear.With 3.23s you should be trapping in 3rd gear at about 6200. You wouldn't ever get into 4th. 3.55s would put you at 6800 in 3rd, so the shift should occur around 104mph/6500rpm.
What rear gear are you running?What was your 60ft?

I think your engine has a lot of potential left in her, but the chassis issues will have to be addressed to make it a safe trip.

As a comparison, the one and only full run I ever made with my 3650lb(me in it), 68FormulaS, it went 93 in the eighth,with 4.30s in 3rd gear@ about 7000. This works out to a 4.3x1.40(3rd gear)=6.02 final-drive ratio.
My engine is about the same as yours, except; I run 10.7Scr on 87E10, and a smaller cam; an old Hughes 230*@050,which is 276/286/110. I run 1.6arms, so lift is .549/.571
When I left the line, the tach climbed to 7000, and I left it there, to the traps. I thought the clutch was done. The track starter said he never saw the tires stop smoking.I estimate the tires started hooking at 85plus mph. I was running 4.30s(IIRC) and 325/50-15 DRs, and street suspension,as born out by the 2.2 60ft.

Super-nice looking Duster! Keep on keeping on!