Foolish design aside, the block casting indicates this is a indeed a Can-Am piece as stated although not a 427 and actually the 70-71 4.5" bore 509 CID!!!
This engine really belongs w/ a McLaren or other Can-Am vintage race piece it's correct for...or may have originally come from?.
Depending on what the other castings and included parts are, considering the values of these Can-Am cars now it may not even be a bad deal?.
~ Pete