From a person who is using a surplus Mitsubishi van for more 4 years now, here are my two cents:

1. From personal experience, I still have to encounter a problem with my van's conversion kit or whatever you may call it. I always maintain that the conversion depends on the quality of how the vehicle was converted and the quality of the materials used.
2. FC? If the Dingo you're looking at has stick shift instead of A/T, I think would be close to 19-20 k/lit. Anyway, I could be wrong.
3. Spare parts? AFAIK the Dingo has an Orion/Cyclone 4G13/4G15 gas engine. Parts for these engines are available at Banawe. AFAIK, the Dingo shares the same underchassis parts with the Lancer so of this would be the case, then the parts will also be easily available at Banawe.