The 2 bolt blocks hold up just fine. Which one are you looking at? The G351? There are several variations...all of which are capable of that amount of HP. I'm running that on a stock block...they usually last 2 seasons give or take before the mains break out.
i asked about the same block over here http://sbftech.com/index.php?topic=440.0 awhile ago,think it was pretty reasonably priced at segedens from memory,the 9.2 deck height was my reason for passing,and not being able to find much info on builds done using the b351