This thread about if you can use a stock block and have success with a 4" crank and w-2 heads.

I have a bunch of high HP engines with stock 340/early 360 blocks, [basicly the same as a 340 casting], in service at this time. I have done them with the 4 bolt caps and my opinion it only adds to the cost of the finished project. Same with roller cams, No more power just a lot more money. In fact a couple times I have removed roller cams from customer engines and installed flat tappet cams and car has gone faster. Roller lifters fail and have ruined many a good bottom end. The only block failures I have experienced were due to other parts failing first.