What stock intake? A 74 318 didn't come with a 4bbl so who knows what you have.

Here's a LINK to the install instructions

It does say "If installing the Street Demon™ on a factory cast iron spread bore style manifold, a spacer may be required for proper throttle opening."

If you have EGR you will probably need a spacer to clear, may be needed to clear the choke well as well. Though with today's gas it's probably needed regardless.

Or seeing as to how the 1406 you have lasted 25 years and it's already installed consider another one, still being made.