Unfortunately, there's nothing much 'out of the box' when you're doing motor swaps into S-10's, especially when you're talking about a small block. Externally, the 400 is identical to every Gen I and II small block. You could put a 283 in and tell eveybody it's a built 377 and nobody would know the difference...lol. That 400 in stock trim is a turd, rated anywhere from 115-145 hp, probaly less now that its got god knows how many miles. To get power out of that engine, you're going to need different heads, intake, carb, cam, lifters....you can get tons of power out of a 400, or any small block, but it takes money...anything over about 350 hp starts costing money. It also depends on how many miles are on that engine. Did you get to hear it run? Typically, industrial/delivery vehicles are put through the ringer, I would suggest a full rebuild, and it will probably need machine work. The small blocks I use are either a) built by me or b) low miles engines that I know the history of. If it's got a questionable history, first thing I do is a complete tear down. Bottom line is that with any used sbc, be prepared to drop a couple grand into it if you're looking for a mild performance build. At the very least, you're going to need to do the bottom end and re-ring it.
The other problem is that you won't be able to register it with the small block in it since it wont pass smog. That means you can't drive it on sunny days or car shows. What's the fun in that? A later model LSx swap would keep you smogable, with tons of power and 20+ mpg to boot, but the cost will go up as well...
I can't speak for Clint, but I just want to make sure you understand what you're getting into, and how much it's actually going to cost, before you're balls deep in a truck you cant drive. As it sits now, you've got a nice, drivable Blazer. I want to make sure you keep it that way when it's done...
You do realize that your 4.3 puts out more power and will be better on gas than that 400, right?
