I think BF use 4mm o/d std tube from the pump to the turbine. The tube supplied with the CARF kit is 6mm o/d and 4mm i/D this is from the tanks to the hopper. Inside the tanks I would use 5/32 i/d Tygon tube.
Other than this you should be fine, with a 300 the Mephisto will do normal aerobatics with low throttle, full power and pump supply is only used if you hover.
You should modify the ducting for the 300 as its a large turbine that blocks the full byepass.
Dave