Need help on a V8 swap

All A bodys from 1973 up from the factory had large bolt patttern six or V8 didnt matter. 72 and older all A bodys from the factory had small bolt pattern six or V8 didnt matter. If you have the bbp setup in something 72 and older then somebody somewhere along the line swapped it. Being these cars are over 30 and 40 years old anything could be done to them by now.