IF you are using a 7.3 idi *i assume you are* you have to change the brackets
Your 351 mounting plates are just behind the Cross member and the 7.3 mounts sit ON the Xmember *holes are all drilled*
Only problem you will have is the driver side front most bolt for the plate is sitting in the middle of the Xmember hole for your gassers oil filter....
i just ran into this with my swap, also 7.3 idi. Actually this weekend going to just change out my Xmember with one made for the D50 and 7.3 combo that i put on my bronco anyways
Hope that helps, you can either weld up that oil filter hole, or i was just going to let it be a hole. 7/8 motor mount plates were secure figured good enough for me