reverseunlocked,
is .3 tonnes legal for landing fuel at an alternate?
You have to arrive at your destination alternate with what is known as final reserve as a minimum. This is enough fuel to fly for 30 minutes at 1500 feet above your destination alternate field in ISA conditions. Therefore you could land with 300 kilos but having that little fuel is too terrifiying to contemplate.
It does depend on weight but the final reserve in a 738 is around 1000-1300 kilos or so.
Al Ain closer perhaps?
Not really. As mentioned above the distances from SLL to AUH, AAL or MCT is roughly the same give or take a very few miles. AUH probably best as it has two independent runways.
V3