Not necessarily... for each yoke, there'll be a number of transmission models its compatible with. You need to cross reference the part number to the transmission nomenclature.
I've never heard of an Eaton Fuller 12 speed, nor am I able to find any references to one via Google. I've driven Eaton Fuller 8LL, 9 speed, 10 speed, 13 speed, and 18 speed transmissions - could you be thinking of one of these? IIRC, Volvo marketed a proprietary 12 speed transmission, and Meritor offered a 12 speed automatic, but not Eaton Fuller.
It's the same as the shift pattern for the Eaton Fuller nine speed transmissions, albeit with additional gears on the low side. For the sake of not wanting to type out a long winded explanation, there is a related link posted - 'Eaton Fuller 18 speed shifting diagram'. Click on that link to see a visual representation of the shift pattern.
Depends on which transmission you have. Eaton-Fuller and Spicer manual transmissions were available, as were Allison automatic transmissions. Additionally, the Ford 6R140 automatic was standard for gas and CNG powered vehicles.
On all Eaton-Fuller transmissions, the fill plug is on the left side of the transmission. You insert the drive end of a 1/2" socket into it, and turn it counterclockwise to unthread it. That's where the transmission oil goes. Eaton-Fuller recommends you use either 50W synthetic, or 80W if you're going with mineral oil.
For the S10 and 1500, the manual was the NV3500 and the automatic was the 4L60E. For the 2500 and 3500, the manual was the NV4500 and the auto was the 4L80E. For their medium- and heavy duty trucks, manual transmissions from Eaton Fuller and Rockwell were available, while automatic transmissions from Allison were available.
Can it be done? Yes. Should it be done? Absolutely not. The manual transmissions available for the F750 from Eaton Fuller and Spicer were synchromesh transmissions - nothing like the unsynchronized twin countershaft transmissions found in Class 8 trucks. Trying to float this box could destroy the synchronizers and ultimately cause the transmission to have to be rebuilt or replaced.
Depends on what you have. If you have a Volvo outside of North America, it has a synchromesh transmission. Volvo synchromesh transmissions are extremely rare in North America, and they'll more often have Eaton-Fuller twin countershift unsynchronized transmissions, where you have to manually make up for the lack of a synchronizer gear.
Installation of countershafts
Transmission options included a range of Eaton-Fuller and TTC Spicer manual transmissions, as well as Allison automatic transmissions (for diesel powered models) and the Ford 6R140 transmission (for gas and CNG powered models only). We'd need to know what transmission you have in order to answer this.
Heavier weight oil might work in warm climates but I wouldn't put it in north of Texas. Eaton specs 50 wt. synthetic in their 18 speeds.
Either a proprietary Mack 18 speed or an Eaton-Fuller 18 speed. Various models of the Eaton-Fuller were available, from 1600 torque to 2100 torque.
Grey, both on an Eaton-Fuller and a Mack 18 speed.