Wondering if 305/70R17's would fit on my 04 Supercrew with the 2.5" front leveling kit? Also using the stock rims.

 

Yes. In fact several people have fit 315/70-17's (35x12.50) on 04-05 F-150 4x4's by using the stock wheels and a 2.5 inch leveling kit. You won't have any problem fitting a 305/70-17 (34x12.50).
Also, welcome to the site!

 

You should be fine, check out my gallery craig41071 I would post the pic. but can't figure out how?? I have 17x8's with 4.75 back spacing and 295/70R17's and a 2.5 leveling kit with no problems at all.