I searched around on autotrader and cars.com and these seem pretty plentiful (the 6.6 diesel, extended cab, 2WD) for under $20k w/under 100k miles. I would go that route because you have a lot of things to think about such as suspension (isn't the diesel much heavier?), plus electronics, wiring harness, doesn't a diesel usually take two batteries(?), fuel system (fuel lines, fuel tank, etc.) plus many things I'm probably missing.
It just seems like a huge headache, a lot of added expenses and tons of unnecessary frustration plus you would never get that money back out of it and if someone plowed into you and totaled it, again, you're never getting that money and time investment back out of it.