idk if this is posted in the correct spot. please move if it aint.

i got a mazda b6t and matching 5 speed stick trans. works good. great even. the car is ragged out. so i need a new hull. just for info purposes its a 91 mercury capriXR2. it aint stock. i payed 100usd for the whole setup and it has much aftermarket bolt ons and exaust, etc. excellent deal for a motor and trans, i think.
i am new to mazda. so if someone could point me in the right direction to find info i would be so greatful.
since the hull is ragged, i need a new one(used) and mercury capri shells are rare. i know a 323 is compatable but what about miatas? they got 1.6L but from what little i can find they are not a b6t like i got, just a b6. Does it mater? will i mess up an auto transmission? is the 4 speed auto trans gonna hook up the same as the 5 speed stick shift i got now? where can i find all this out?
please someone help me. Ford sucks, they dont even make a manual for this car anymore. and mazda cant tell me anything cuz its all Ford numbers(from Ford australia, to make it worse)
is anything else usable besides a 323 body?
where is some good literature so i can educate myself, i have always been before i learned about what these little 4 bangers can do, been a big block, muscle car type.
please help.