Very nice truck. As Baldeagle said, it's definitely not a '47, or '48 model,with that inside cab fuel tank, & I agree with the '49, or '50 model guess. The 400, 450, & 470 series trucks use the larger front fenders as yours has, plus will always be either 6 lug, or 10 lug, front, & rear. Daytons were standard on the 400 series, & optional on the 450, & 470 series. Check out
www.oldgmctrucks.com , & you should be able to look up the ID number, & determine the exact year. If you decide to remove the Fire apparatus, i'd be interested in those rear fenders, for my Holmes Wrecker body.