Who tells you that?
prior to 1977 or so, Oldsmobile cranks were supported in the block by main bearings which were tied to the block with webs of cast iron. Fatter where the bolts go, obviously, and thinner webs in the middle between the bolts.

In a weight loss program starting around 1977, the main bearing support webs were produced with holes, thus no longer solid. More like three posts of cast iron tying block to the main bearings and crank. Blocks with the A suffix typically have the open main webs. 3A = 350, 4A or the far more common 4B = 403, etc.

So, the Bullsnort comes when the rumor started that "some" 403's were cast without the openings in the webs: the "Solid Main Web 403". So, for many years we all looked for one. I started offering a reward just for proof they exist- one photo. After a year or two, it became obvious that no photos were ever going to appear because none of these SMW 403 "4A" blocks exist. Meanwhile I collected dozens of stories, all with the same general format- ending in "but I can't get photos right now." Only the details changed from story to story. So after upping the reward 10x per month in the club newsletter until it reached $1,000,000.... on 02APR2000 I declared the thing a myth so we can all quit looking for these Unicorns.

 

And, I keep answering Chris that I have a bunch of them, all are E blocks bored .015" over. lol.

 

Hrmmpf. He's got you there, rocket scientist.

 

Right after the block casting becomes "4A" and the deck height and main bearing size matches the usual 350's.

*scoff*