Hi mate, I'm currently going down the ls path, what I have learned so far is if you plan to get the vehicle engineered, the motor will need to be the same or newer than the car you're putting it in. This limits you to LSA and maybe ls3, although I'm not sure if the ls3 is still in production? I'm putting an ls1 from a 2004 holden adventra in my 2004 3L. I could put any motor from 2004 on in it but I'm a tight ass and cant afford a better motor(not that the ls1 is a sh!tter anyway lol). You will be up for around 4-6k in Mark's 4x4 conversion parts, plus the cost of the motor, it's much wiser to buy a whole car and pilfer it for bits such as ecu, transmission and even accelerator and throttle cable.
As far as kms out of a tank, as I said, i have bought an holden adventra, I'm going to drive it for 12 months which gives me time to source all the other bits I need, and take the 3L out of the patrol. I can get everything ready and then when the time comes I should be able to swap it quickly. Having driven the car around for 2 weeks, I and getting 16-18 lph driving short trips around town, have got as low as 11 on a semi decent drive but haven't done a full tank of hwy kms yet. I'm getti g between 300-450ks from 60L however the cars fuel tank is only 70L and I don't like letting them get low. Your patrol should hold twice that amount, and if your only doing hwy ks I would take a stab and say you should almost get 1000ks per tank if you drive it moderately. I hope this helps, if you do go.ahead with your plan I look forward to seeing your build thread mate.
Cheers
Rusty
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