1971 rally sport 4 spd. no motor

how can I tell for sure if the car was/is set up for a big block or a small block,.

I will have to change front springs if I get it wrong.

It is a Air cond car, some one told me that the ac unit in the firewall had to be a narrow one to make room for the bi blk valve covers etc, I know all big blocks came with rear sway bars but the car is to far apart to tell about the sway bar option..what else please.