OK now we are getting somewhere now I am guessing and please correct me if I am wrong. If the airplane is what I suspect it does not have ailerons and has a wingspan of a about 45 to 55 inchs. This airplane was intended for engine in the .15, .20 class and certainly no more than .25. A Fifty, any relatively modern fifty is serious overkill and will not provide you with the nice trainer that is perhaps needed. It is going to be so nose heavy with that long nose moment that it will be difficult to get the CG where it needs to be.

The reason for the substancial down thrust is this airplane originated in the sixtys when single channel rudder only systems were the norm. No elevator! so the substancial stabilizer negative incidence in concert with the downthrust provide considerable pitch stability for rudder only flight.

John