lol, probably doesn't really matter what kind of oil you use, they will last forever anyways.
Id suggest using some 10w30 dino for, 1, its cheap and readily availible, and 2, because it has higher mileage and would be more likely to consumption.
story here: a bunch of guys in this car club/internet message board I visit got about 250,000 miles out of a similar truck. It eventually threw a rod right through the block, yet was able to idle its way to its final resting spot a couple miles away on 3 cylinders.
I am familiar with the 1.8 engine in the miata and if this engine is simular it loves a standard 5w-30 or 10w-30. If it doesn't use any oil I would recomend Mobil 1 10w-30 and 6000 mile changes. It it uses oil I would go with the delo 400 15w-40 which is a great dino oil and reasonable priced at walmart.
I have a Mazda 626 with the 2.0 liter 4 banger and have used nothing but Mobil 1 5W-30. The engine seems to love it. Before I knew about this board I used a Fram oil filter and had some start up noise. I switched to the Mobil 1 filter and the noise went away. The filter is mounted upside down so a good anti drain back value is important.