If the fan area is 4" across then shoe horn that puppy in thru the wing saddle area, with the numbers you gave your outlet to FSA is around 87.9%. That's close enough to the 90% mark your looking for, just make sure that your intake is not smaller than the FSA. Plus I would put the tank in the wing to help maintain the CG point, on such small models the CG is very sensitive, espiecally since the fuel we're putting in can weigh 25% of the models weight.