There is only one production block that you'll find for the Windsor 351. It is basically a Raised Deck 289/302/ 5 liter block. A few, very few, of the earliest blocks were very slightly different. If the manifold you were sent was too narrow, it was for a
302 and not your 351. The confusion lies in the fact that the 351M came with a 400M block. This was a raised deck 351
CLEVELAND. That engine was never to my knowledge used by Crusader. Your engine is NOT an M or a Cleveland, again, it's a Windsor.
Frank/RebopBristol, In ( by Elkhart) 
