Is it hard to find 4-speed Demons? Or is it just my luck?

I agree; just buy the first nice complete one you find, and convert it to whatever you want it to be.
Lock-Up Automatics are nice because the TC acts like a two speed, and the LU is an easy half gear, so your TF acts like a 4.5 speed. With a high enough stall (say 2800) you won't even notice the wide splits.
______________________
If you think yur gonna row gears on the street, with an A833, yur gonna have to short shift, so install a small-cam 360 at the least.
28" Tires are about the tallest you can install in the short wb/ big tub cars, so traction is gonna be a big problem.
With a smaller engine, you will have to wind it up, so be prepared to go into the high 3-series gears. This might allow you to get into third before 60 mph coming from WOT in Second, but 65 mph is gonna be right there, so unless you don't mind risking a speeding ticket; 65 is where I shut down about 99% of the time.
Just tooling around my 360 likes to be shifted at no more than 3000. With 3.55s this happens at
25,35,48, and 67mph. That's a long pull from 48 to 67, so you guessed it, that's why I have a 360. And also because shifting at 3000 the Rs fall to 2160, so yur engine is gonna need some low-rpm pressure, to climb out of that hole.
With a 4-speed, you have to be careful; Too much rear gear and the car gets a lil buzzy on the hiway.Too little gear and you can't drive them very slowly. With 3.55s and a 2.66, low gear, and 26.7" tires, your slowest speed is; 6.3@750rpm, 5.5@650, 4.6@550. You cannot drive any slower unless you slip the clutch.... so that will only sorta work for a few seconds atta time.
But 3.55s will get you 65@2900, so yur already strapped for gear.
With a manual trans you really need a Fifth gear.
I solved my problems with a 3.09 low gear and an overdrive. Which simultaneously solved the previous long pull in Third gear. The shifts now being at;
22,35,48,62 and then into 4-over at 65=2260
This rpm is about as low as you wanna cruise at with a warmed up 360. It is high enough to be reasonably efficient and low enough to not be buzzy. And with the 3.09 x3.55 starter gear 550=3.99 mph with those 26.7 tires.
Now with an A999LU, you can use 3.23s for 65=2640, and no limit on how slow you wanna go.
Or the A500 with 3.91s for 65=2200, and still no limit on how slow.
I have a soft spot in my heart for the Demon; IMO the 71 is probably the epitome of good looking Mopars of the era. But even the 6-banger models are getting pricey.