[Jacques Reed]

[QUOTE
The cab floor may also give help. do the openings for transfer case shift lever look factory or "gas-axe" made?[/QUOTE]

Hi Luke,

As Grant said there are a lot of pointers to a gun tractor chassis and the floorboard would be a good indicator if it was an original F15A with the single speed xfer case.
As shown on the attached photo the F-15A floor has just a single notch beside the fuel tank selector valve for the transfer case selector lever and no hole in the floor to the left of the valve where the two speed lever would be. If you have a slot, and a hole, for the two levers it definitely was a "gas axe" job.

I had an F-15A with a two speed xfer case and 20" wheels but that was not an uncommon civilian mod. The holes on the crossmember where the transfer case attaches to it were also elongated to fit the larger 2 spd xfer case mounting pattern which is another giveaway that it was originally an F-15A chassis. Another indicator would be the diff markings. An F-15A has the ratio "6-39" (pinion-crown gear teeth) stamped on the diff housing opposite the pinions of the diffs and vehicles with original 20" wheels have "6-43" stamped at that position, 6-5:1 versus 7.16:1 ratios.

There a few a few gun tractor specialists on the forum who no doubt can shed more light on it. I'm hoping it is a gun tractor.

Cheers,