318 engine identification

That’s the first I’ve ever heard about the thick walls being identified by the four motor mount bolt lugs. Do p-car 318s only have 3? My ‘74 318 has 4 mount lugs same as both my 340s - I thought all smallblocks had 4 lugs per side?
Not all.
340?
My '70 340 has 3, a lot of 318's had 3, 360 were 3 etc.