Maybe I am seeing things, but the truck in pic. two looks like it has dual wheels.Yes, you can use the photo of my truck, or either of the ones below.
The tank is 400 gallon, with an additional foam tank - which I think is 40 gallons. My truck is a 530C, last of the series, it has a 750 GPM midships-mounted Waterous pump. Also notice the foam gun above the cab. The 530C trucks were powered by either the LD-465 or LDT-465 Multifuel engine (many folks mistakenly call these diesel), and have dual rear wheels.
The 530B at a glance looks just like this - however without the foam gun. Internally, the 530B has a 500 gpm pump. Although the bed looks like the one on the 530C, almost none of the body parts interchange. The 530B can have either single or dual wheels, and can be powered by either of the engines listed above, or a LDS-427 Multifuel engine, or a OA-331 gas engine.
Below is a photo of a 530A. Rather than a midships pump, the 530A had a pump mounted on the front bumper (so do lots of "home-brew" fire trucks). Whereas the Bs and Cs had compartmented bodies with internal stowage, much of the gear on a 530A was hung on the outside of the truck. All of the 530As had OA-331 Reo or Continental gas engines and single rear tires.
The 6x6 military tactical fire truck prior to the 530A was based on the GMC CCKW (whereas the trucks listed above were built on a Reo-designed chassis that could have been built by any number of different firms). Depending on whose reference you use, the GMC was either a Class 335 or Class 530. I'll post a photo below, just in case.
Hope this helps,