Mike,
I've converted some of these to Kadees. I did just as you suggest and installed styrene to mount the draft gear box on the "A" end. There is just enough material on the "B" end to mount the Kadee. It's a pretty straight-forward job. I've similarly converted a few of the older MTH cars.
On the Lionels, I replaced those absurd factory trucks with proper roller bearing trucks. Though I often install two-rail trucks in my conversions (if I ever build a two-rail layout, I'll have a lot of rolling stock ready to go) for these cars I just used three-rail trucks I had on hand. I ought to try to sell the Lionel trucks, I suppose.
I'm a Santa Fe guy, and I only run these coal porters occasionally, when the mood strikes me to represent the BNSF era for a little. Somewhere I have a video of a short coal train of these.
RM