Here are some pics I have so you can see for yourself. The ribs are very obvious on the 70s 340 manifold, you can also see the difference in "rise" height:
View attachment 1715129438 View attachment 1715129439 View attachment 1715129440 View attachment 1715129441 View attachment 1715129442
I think Mopar added the ribs (1970s) to add some rigidity (to preclude cracking) and to give you a place to attach the spark plug "metal" shield. I have no idea why they changed the flow design (but only slightly).
Treblig
