the liquid cooled engine is the way to go. you can put a fan cooled motor in a liquid cooled sled but if you put a liquid cooled engine in a fan cooled sled you also need to put all the cooling neccesities in also
Lots of luck with whatever sled you get! It would be no problem putting a fan cooled on a liquid cooled sled, but to put a liquid cooled on a fan cooled model would be lots of time and money, You have to add all the liquid cooled parts with it. Good Luck!! and have fun.