Rick,
I would think attaching the slide channel upper end to a metal crossover would be more factory correct. In your case it would help reduce the angle of the slide channel. The steeper the angle of the slide channel, the steeper it would be to slide the spare up into place. I need to take a pic of my setup.

This thread is also reminding me that maybe it's time to excersize my slider setup, grease the channel, etc.

Craig

My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear
My truck ....... Respect The Rust
If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.