Engine identification help

[Cragmor]

I pulled the ID and casting number from my block. I have a 76 C10, but the engine appears to be a 75 350 pulled from a C20, based off of the block ID.
V1007TXR 1975 350 fwrd cab c-20 to 3500 165hp 4bbl l ls9

Casting number appears to be missing a digit. I have 39700_0. Looking up what I know, it appears that the digit should be a 1. That fits the year and CID. What I was hoping to learn was if this was a 2 or 4 bolt main. So, hoping some guru hear can take both bits of info and determine if that since the engine came from a heavier duty truck, would it be more likely to have a 4 bolt. Or, during the mid 70's was it just chaos, lol.
Just got the truck so still sorting out what I want to do. Have not had a chance to even consider pulling the oil pan yet. I will if need be.

 

[bucket]

If you are doing an oil change, you could possibly look at the main caps with a boroscope, through the drain plug hole.

But in my opinion, there's no need to worry if it's a 4-bolt block unless you plan to build for big power.