They make 289/302 gaskets that do not have the funky L-shape. 
Available at your local autozone, oreilly's, etc... 

or here...
https://www.rockauto.com/en/catalog/ford,1968,mustang,4.7l+289cid+v8,1132322,engine,intake+manifold+gasket+/+set,5424
 

Last edited by Michael H. (10/15/2018 1:30 PM)

"IF a little bit works then.............alot aughta be better!"
Cut it out!
So long as you have sealing surface around the port you will be fine.
The big question (for somebody is) whatz the porpoise of that L-shaped hickey?!
6sally6

I had a heck of a time finding a proper gasket.  The one pictured is for Fords from '78 on I think.  They changed the water ports, because the early ones were almost square.  Don't use that gasket on an early engine; it won't seal right, and I worry about overheating with partially occluding the water ports.  Those gaskets work on the 5.0s, which I think is why everyone has them (I had two sets of them lying around myself). 

I used a Mahle MS15172 I bought through Rock Auto for $8.20.  They looked exactly like the ones I removed from the engine, which was a Ford reman I bought in the mid '90s.  It didn't come with the intake, but I think came with the gaskets to install it, or maybe I bought them at NAPA, can't really remember.  Mahle also lists a graphite version, and Ford used Victor Reinz gaskets for a long time, so I'm wondering if Mahle maybe bought Victor?

On the install, you don't ever use silicone like that on an intake.  Use a thin film around the water ports on both sides only.  Stick the gasket in place with Gasket Tack from Permatex.  I then use Aviation Form A Gasket around the ports on both sides of the gasket.  It takes a while to set that all up, but it provides the best possible seal on all fronts.  The gaskets don't move.  The water ports don't leak.  The intake ports don't leak, but if they do because the bolts loosen up, just cinch them back down and the Permatex will reseal itself.