Very early 6.9's may have been 22:1, but most IDI's 6.9 and 7.3 including the Factory Turbo in 93.5-94.5 was 21 or 21.5:1.
The 7.3 PSD in 94.5, which is a Direct Injected, Turbocharged engine that is designed completely different than the IDI was 16 or 17:1, because they were designed with a turbo in mind.
Putting a turbo on an N/A engine is not an issue. Keep the boost reasonable 10ish in a 6.9 12ish in a 7.3 and it will hole up well. Many IDI's had a turbo kit added to an N/A engine, including mine. decades ago and are still running well with tons of miles. Now, wanting big numbers, then there is work to be done. My truck, has been worked most of it's life, is has ~150,000 miles, and has an early Hypermax Turbo on it, and the biggest problem with mine is electrical, not mechanical due to the turbo. Then engine needs a water pump, and the engine electrical fixed, and tires. The engine would go anywhere I wanted to go, if I could keep coolant in it and the tires not blow (yes they are that bad).....
They will tow well, just not necessarily fast. I remember back in the day, when these were still fairly new and we didn't have the improvements Mel. Russ Justin and Wes have made, hearing an N/A IDI will tow anything at 35, and one with an added turbo and the 2 flat recommended increase in fuel at 45. These speed were at max loads, not towing a lawn mower.
One other thing to remember, these trucks were designed when the national speed limit was 55. I've seen may posts with people saying my trucks seems to work best in the 55-60 range, it doesn't like 70-75. Well, 55 was what it was designed for. The newer trucks were designed for 65-70 speeds limits. The RPM's my IDI runs at 55-60 is what my 6.0 runs at 70-75. But the 6.0 has a different gear ratio, larger brakes, and more power to reach that goal. An N/A IDI was 185 at the crank, a 6.0 was 325. The statement of my truck won't keep up with the new trucks..... well, it wasn't designed to. Not saying you can't make them run that well, but like Wes
@Thewespaul said in one of his threads, he was towing a fairly heavy trailer at 80 with no problem with is shop truck, but look at what he has done. You can make an IDI a solid tow truck. But keep in mind, you are dealing with an engine that was originally designed in the 70's, and put in with a goal of running at 55 MPH.
Please don't think I'm knocking the IDI, I'm not. I like them, and the trucks they are in. My oldest just picked up another one for a song. But keep in mind what you are dealing with. Not just in these trucks, but across the board. The fastest, big V-8 muscle cars that were in the 400 Cubic Inch range, and were the fastest things on the road in the 60's 70's and early 80's would have their a$$ handed to them today by a 4 or 6 cylinder. Just think, the "big 3" are now in the 400hp range factory, up from the 200 range in the IDI's and 7.3 PSD.