The 65mph quoted would be your total exhaust veleocity, therefore only a small increase over freestream speed.. Personally I'd remove the centrebodies and reduce the engine diameter, this will reduce drag and still give you the same cross sectional intake area.
The way I approach these things is to start simple by assuming the engine is operating under an 'ideal cycle', this means that no heat is lost, (aqdiabatic) and any compression and expansion is isentropic and fully reversable. Then it just a simple case of appling perfect gas laws at each stage, and using a few assumptions, (like the combustion temp), you can get an idea of the engines performance.
When the engine is operating under steady state conditions, (constant throttle posistion, steady airspeed ect), and with good estimates of each components efficencies then its not that inaccurate. I wrote two programs to simulate the steady state and transient performace of small gas turbines, and the steady state model was within about 5% of the experimental results for the temperatures, thrust, fuel flow, mass flow ect.. The transient model was less accurate, when compared to the engines actual performance during say a minimum to maximum throttling. This is mostly due to the heat transfer occuring in the engine as it moves from one steady state condition to another, which I'd neglected in the model at the time.
Anyway I cant write anymore because I'm literally running out of the door before I go on holiday
.. Good luck though!!!