...the ones in my ranger with the coil seats are 2.75...i want to say that they could have went with 3's but they didn't have any in stock...
...that does bring up a good point as to not only check on the alignment cost, but the availability of 2.75 bushings...now these bushings are eliptecle and they are adjustable compared to a fixed bushing...

...here's a link to the f150 coil seat thread...i hope this helps...