V-12 Detroit in a M813

I have a V-12 Detroit diesel and I would like to put it in my M813 and it looked liked it would fit but I am not sure can anybody help me on this. The cummins 250 in the truck is already about the same length I am conserned mostly about the width just in case you wanted to know it is a 71 series any help is appreciated

 

                                                                  Thanks

                                                                  Josh

                                                                  M35A2C

                                                                  M813