Hello, 
I am new to this forum, and to the Y-Block. Interesting engine. I'm freshening a 312 Interceptor marine engine from an 1964 wooden ski boat. I've read about the main bolts being shorter in the 312, and about bottom tapping for longer bolts. This engine makes 215  h.p, about all the transmission can handle, so it won't be a hipo build. Are the longer bolts necessary for my needs? What fasteners would you suggest? Thanks in advance.