Just realized your probably talking about a 351W block.
The increased height of the block will cause problems.
If using the stock hood with stock engine mounts, the cobra manifold will not clear the hood. You can use 3/4" solid drop mounts, but this will limit your choice of oil pans, unless you are ready for a tubular K-member. For example, my Canton 7qt pan did not clear the stock K-member with 3/4" drop mounts.
You can have the upper intake manifold modified to fit. With some careful measuring you should be able to find the correct measurements to give to a machine/weld shop.
Or you can simply install an aftermarket hood to gain the needed clearance.
Hope one of my responses answered your question.