alectheamazing

hey everyone. so first of all this is my first subaru and i dont know a whole lot about them so i will probably be asking alot of questions!!!! first off, i just bought my white '05 sti for 6500 its missing a tranny and all the turbo hoses. the hoses are no big deal im just going to buy new ones. my big concern is that when i went to pick it up it had a regular wrx 5 speed in it instead of the sti 6 speed. i was reassured by the guy the engine ran. being skeptical, i asked him to start it. when i turned the key, i heard one big clunk but the motor would not turn. would the wrx tranny keep the sti motor from turning over? and if not, would the ej20 trans work until i got an sti tranny? any insight into this problem i would greatly appreciate.