My 1993 Chevy Silverado must have been an exception. Right before I got rid of it, I replaced the oil pan gasket on it (PITA!) and it was a 2 bolt main. Got rid of it because when I started it, there was a nice main bearing clatter for about a 1/2 a second. It had 200k on it when I got rid of it. Anyway, don't mean to ramble on and jack your thread...just my .02 cents.
If you can find your block number, I can tell you if it is a four bolt or two bolt.
I can't. There are vin decoder websites out there. I don't know if it will tell you 2 or 4 bolt with the vin decoders. The casting number is located on the driver's side, top rear of the engine block. It is right behind the head. This should be a 7 or 8 digit number. I am going to throw a wrench in here though...some blocks have the same casting number but may have 2 or 4 bolt mains. If you find the casting (starts with a 140... I think for 92's) number, I can tell you what it should have though.