Make sure you have the 3200 rpm gov spring so that you can cope with the wider gear spread and not force the getrag to pull heavy at low rpms. It was a bit of a problem even with my 354's and the spring fixed things nicely. My pilot shaft is kinda loose because I did not replace it when I did the rest of the tranny. So far it is holding up but making lots of vibration at low rpms at load. You may find 307 a bit tall for delicate work with a heavy trailer but you will love it around town and on the highway. I seem to remember that the 307's are too different to fit in the case so a complete swap is required. The taller gears make the truck run MUCH quieter at highway speeds.

 

I haven't had a consistent set of results since I let the truck idle a lot now that it is cold. The only long trip I took was about 300 miles round trip and I got about 23 on winterized lsdf. The auto at best would give just shy of 18 and that was on a good day without being generous with the loud pedal.