OK, I know this is new to you.

ANY vehicle, full-size airplane, boat, car or whatever is a balance of power and weight. You seem intent on installing .46s on the Transall, which would probably work, but the airframe is designed and optimized for smaller engines. OK, I've been guilty of overpowering myself - I installed a Super Tigre .46
in a Das Little Stick (span 46") and it went vertical, unheard of in the 1970s. It was also terribly nose heavy, and needed lead in the tail. It makes as much sense as installing a 454 Chrysler Hemi engine in a Honda Civic

Matador, it sounds like you might need some more practical experience actually flying R/C before you spend the time and money on something as complex and critical to operate as the Transall (or any twin.) The Hobbico Twinstar (.20s are PLENTY) will give you twin experience on a minimal cost and investment.
Good Luck! Russ Farris