Need '58 GMC 336 engine cast number!

[dyno]

I just bought a 1958 GMC 150 and am trying to ID the motor. The truck should have come from the factory with a 336. My cast number on the block CLEARLY reads 523283. That number is not found on any chart. The closest number, one digit off, is 523293 which is the code for a 347. I tried to find a cast number for 336 on the internet, but no charts show it.

I have seen other posts with guys having the same engine ID problem, with the same 523283 block number as mine.

Does anyone have a 336? If so, what the hell is your cast number! It's on the passenger side, close to the dipstick tube.

Thanks! Dyno