Running a diesel engine on JetA1 is dependant on the tye of injector pump. If it's one of the "old generation" like Ford/Perkins etc then you should have no problems. The more modern engines use a common rail system that runs at higher pressures and these pumps are more sensetive to the lubrication requirements of the fuel.
We had an old Ford tractor at work that ran on JetA for almost 20 years with no hassles and one of the engineers had an Isuzu pick-up truck that lasted about 6 months before the pump failed. I ran a Mercedes 240D for 9 months on JetA before I sold it and it was fine.
I would think twice before using JetA in a modern vehicle due to the new pump technology, but if you have a garden tractor or an older vehicle, go for it.
I would use SAE30 or 40 to mix into the fuel for lubrication if anything, but remember that if the vehicle stands for a while it will settle out so a bit of jerky driving in the beginning to mix it in may be in order.
