This is what I found on goodle. Not sure if it is 100% correct.
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The G351 is a dry sump only non-siameese bore 9.2" block with nodular iron caps. The R351 is the siameese version. The S351 is the 9.5" dry sump siameese bore block.
The V351 is the siameese bore wet sump 9.2" , and the W351 is the 9.5" wet sump block.
The "sportsman" blocks are B, C, and D351.
The D is 9.5", the B and C351 blocks are 9.2" with the "C" having spacers to run the Clev. 2.75" mains.
The Non siameese blocks will only go to 4.060"