20x9 on 6 lug '68

[FirstGen]

I have used the search feature on this forum and found plenty of links relating to this question but no exact answers so I thought I would ask straight out.

I have a '68 long step with all stock suspension, 6 lug, coils all that. I would like to run 20x9 with a 295 40ZR20 all the way around. Is this possible with a 3/5 drop? And what backspacing would be reccomended for front and rear? What is the max and min backspacing for these trucks?

I've read that the 71/2 rear ends often were wider by about 1.25-1.5 inches so does that mean that the narrower rears will stick in further if you use the same backspacing on the front and rear?

If nobody can answer my question directly, posting your current larger wheel specs (17's and up), tire specs, and backspacing with any relavant suspension mods would be greatly appreciated!

Thanks in advance!!!

[FirstGen]

ANYONE??? HELP!