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so many options you have., oil cooler, you dont need. so remove it orrrrr if you really want to use it use purchase a TD radiator, will fit in your current mounts and the engine oil cooler pipes will fit no problem
Gearbox wise, the strongest box is the LT85, not the quietest but designed for the V8 and fits perfectly. if your purchasing new then a R380 would be a nice upgrade but you'd need to change / modify your tunned / seat box to accept which ever gearbox you decide to go for.
A two hole tank is the better option, i have done both. you can use the 1 hole and put a intank pump but i found i had to loose the low light as i needed the connection to run the pump. External pumps are noisey.. a two hole tank does work better.
The Efi system is nice and simple to fit. only a hand ful of wires to fit. so no drama there.
Fans - what is the purpose of use? off roading? then the biggest fan you can fit or twin. on road? then just one fan will do or why not fit the viscous?
this is only one way. but there are a few option you have.