I've got a 4-bolt 305 block, but I had to build it myself. I bought a set of add-on 4-bolt main caps on ebay, and installed them and line-bored the block to fit. I was planning on building an experimental short-stroke engine that was expected to turn around 9,500 RPM with a roller cam and a set of trick connecting rods. The bore & stroke I was planning on using would end up at around 250 cubic inches, and the idea was to keep it wound up and outrun a bunch of 350's on a 5/8 mile alphalt round track. We were limited to a single 2-barel Holley 350 CFM carburetor regardless of engine size, and I figured a 100 cubic inch smaller engine running 1,500 RPM faster that the competition might get some attention. The track changed the rules before the project got off the ground, so I'm still tinkering with ideas on how to squeeze a few more RPM out of the design.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!