If anything your headers will set too low. I have 302 headers on my 351. I used the latest frame mounts that CR had which dropped the engine 3/4" and then still had to cut the body opening another 1/2".
My only real issue is that my
oil pan only sets 3 1/2" off the ground and it is lower than the front cross member.
You can always put a spacer between the frame and the frame mount to raise your engine a bit.