2003 F250 crew cab, short bed, 4x4. from what i've read here my wheelbase is 156" and i will need NON-tapered blocks. replacing 2" blocks with 4".

 

Yes Flat-Blocks is what was required on my 2006 F250
The kit I installed (Pro-Comp # 62667K) came with Tappered-Blocks which put a big pinch in my Driveshaft @ the Pinion & a vibration
Lets say ProComp was adamant i needed Tappered but I was even more persuasive about the Flat-Blocks (sent them the following pic's) & they agreed to send me Flat-Blocks free of charge....
Now she's perfect

*Pics to follow

 

Here's some Pic's showing the difference, after this most other people on here seem to have Flat-Blocks also so I say u need Flat's.....
Hope this helps

 

Wow!!! It doesn't get any clearer than that! Thank you very much.

 

King-bRanch, have you experienced any vibrations or shutter since adding the blocks?

Looking at Fords TSB to add the blocks, they replace the carrier bearing and even the drive the drive shaft in some cases.