Rims, tire sizes, 4/6 drop HELP!

[GreyHoundSteve]

I tried this question on the suspension forum and didnt have much luck so let me reword it and try here. I have a 67swb and am planning a 4/6 static drop and am in the market for rims and tires. I found some rims i like, they are Boss 311 and available in 20x8.5 +10mm offset & 5 1/8 bsm and 22x9.5 +12mm offset & 5.682 bsm and was thinking about using the 20"s up front and 22"s in the rear. Will these rims fit on my truck without any problems?

When i used the tire size calculator it said that i shouldnt have that much difference in rim size...... why is that and does anyone have any info to offer on this and what problems it might cause?

Next, if it is possible to run this combo, what size tires will fit would you recomend? I want a sidewall of about 4" so i was thinking 245/40/20 up front and 285/35/22 in back. That would give me a diameter of 27.71 in front and 29.85 in back, would that work without problems?

I would like everyones opinions on this because i know very little about tire sizes and i know even less about what would fit. Please share your experiences and problems i might run into. I would be willing to tub the rear if i have to but would prefer to find a combo that would fit under the truck as it is. If you guys think that i will have alot of problems with 22's in back then i guess i could run 20's but i am concerned that an 8.5" rim wont be able to put enough rubber on the ground. What do you guys think?

Heres a picture of the rims i want to use.