Gimpy
Oops some of this was already posted while I was away from the reply I had part done.... Also, if the ad Westy posted is for this truck you may not need some of this.
If you are not sure the truck has a correct key or whether the switch has been monkeyed with you should take an ignition switch with you. Many switches have four terminals but the M915 series trucks have five as one is used for the fuel shut-off solenoid. The Airtex brand 1S6152 is a correct commercial ignition switch. It has the fifth contact for the fuel shut off and is about a ten minute job to swap.
Yes, if you tow it you'll need to pull the drive shaft. The U-joint at the forward rear axle is the style that has caps over the journal ends. You can disconnect it there and not have to deal with the transmission leaking. There is a round frame cross member above the shaft where you can strap the shaft up out of the way. I recommend using another small strap or rope through the front U-joint at the rear of the transmission to keep the drive shaft from coming out. There's no shortage of places to tie off to.
The M915 has glad hands on the front bumper so if they haven't been broken by GL or anyone else you should may able to slave the brakes. I suspect that an M915 series truck could be a PITA to flat tow due to the front wheels wandering but haven't ever tried it yet. Does anyone know for sure if the air brakes can be slaved from an older MV? The older stuff uses air to set the brakes and the brakes on the M915 bleed air to set them. I've never tried it so I'm in the dark....
The M915 has much bigger towing shackles than an M809. Where the M809 bumper lug is 1-/38" wide and it uses a 1" pin the M915/A1 uses a lug that's 1-3/4" wide with a 1-5/8" pin.
The radiator guard and cowl are a lot closer to the shackle (2" from the pin center to the radiator guard,) than a tactical truck's are. Having some method,like axle clamps and a tow bar to keep the tractor from moving fore and aft will be important if you tow with the front end in the air. The front axle is an I-beam and I think the small axle clamps will fit it fine.
The front bumper is so much lower to the ground (20") than a tactical truck that you may be doing a lot of lifting to pick it up high enough to tow it with the front wheels off the ground and a tow bar with axle clamps. Since the M915 axle is closer to the bumper than a tactical truk that may not be too bad though.
Let us know if you need the commercial part numbers for any of the filters. The truck has spin on oil, oil bypass, fuel, coolant and external transmission filters. A strap wrench can be handy to get them off.
The battery setup is a hybrid 12/24 volt hook up. If you need the wiring diagram or a picture, let me know. You can get by with two batteries even in the winter. The compression ratio is enough lower than an NHC-250 due to the turbocharger that they start a bunch easier than an M809, especially when cold. I've never used the ether start on mine-I don't even know if it works.
I hope some of this helps.
Good luck.
Lance