i am planning on replacing my 2” factory block with a 4.5” block on my 06 F250. Do I need to worry about the carrier bearing, since it is only 1/2” or so higher than a F350?

Ok, I read 1/4” for every 1” of lift, so I guess 5/8”?

My guess would be you will probably need them and in my experience with a few different trucks you need more than the 1/4” per inch of lift rule of thumb too You shouldn’t need more than 1/2” of shim though. I would just get a couple of the 1/4 shims and have them ready when you change the blocks.

you need to use flat blocks with 2 piece drive shaft trucks like the op has.