If you're serious about building power, especially power that lasts beyond one dyno pull, you know that a two-bolt main block just doesn't cut it. High-horsepower motors throw the crank harder, and with a measly two bolts holding your guts in, eventually something is going to fly out, crack, stretch, or flex.
When it comes to strength and bottom-end survival, four-bolt mains are a necessity. The only problem is that most of the four-bolt main blocks are either still in use or are already in someone else's hot rod. But here comes the good news: There are plenty of two-bolt main small-block Chevy 350s and 400s just waiting in your local junkyard, and Milodon makes a two-bolt to four-bolt main conversion kit, so you can play hardball with less hassle and less money. The kit will actually make your engine stronger than a factory four-bolt.
Milodon's kit comes with much bigger and stronger main caps. The splayed outside bolts connect to the block in a much meatier area than a stock four-bolt main cap, decreasing the likelihood of cracking (which four-bolt 400s are notorious for). PAW in Chatsworth, California, sells the kit and offers to install it as an extra when you buy one of the company's engines (that way you don't have to make an extra trip to the machine shop). We went to PAW to take photos of the conversion on a two-bolt main small-block Chevy.
If you're putting together a small-block 350 or 400, Milodon's conversion kit is a great idea. It's not the type of install that you can do at home (unless you've turned your guest house into a machine shop), but with the right tools and gauges, your local machinist can do the conversion for you very easily.