I agree. 4-bolts are stronger, but its not a big deal until you get to 450 or so hp. I've seen 600 hp on 2-bolts but I don't recommend it.
Don't fret over it. Unless you're going nuts with revs and hp, a 2-bolt is great. If you find a deal on a 4-bolt, get it. If not, get a 2-bolt and run it as-is. The 2-bolt blocks have a little bit more metal around the mains than the 4 bolts, so what you can do is have a machine shop drill and tap a 2-bolt block for 4 bolts and be a bit stronger for not much money.
In order of strength, it goes 2-bolt, 4-bolt factory, and a very slight edge goes to a 2-bolt modified for 4 bolts. Call a machine shop and ask how much that service is so you can factor it into your research. Keep an eye on Craigslist and the local paper. I have three 4-bolt engines right now. One I found in the paper for $250, another I got free when I picked up a free wasted boat (and sold the boat and trailer for $400
) and another I got free from a friend who is going through a divorce
Anyway, they're around. 2-bolts are fine for 95% of performance street engines. If you're going nuts and building a really hot 500-hp engine I'd go 4-bolt, but 350hp won't know the difference.