So I'm from CT, which is a weird state to be sure. I'm juggling a variety of engine builds right now, so bear in mind that this build idea in no way applies to me. That said:
I've seen a million posts asking about building 383's. All of these begin with a well intentioned kid looking to add some power to their new ride, and end with "get a t56".
I'm not trying to put anyone down; I was one of those same kids. I just picked up my trashed 4th gen the other day. I ended up deciding to use the lt1 it came with (mostly because it was the first 350 I've ever seen run). It's a relatively easy swap all things considered, but it did get me thinking.
The logic behind the 383 is usually that it costs almost the same as rebuilding the 350. But if that's the case, why not suggest finding a used 7.4l Big Block?
The price for rebuilding seems similar, and a bone stock 454 is just about all a t56 can handle. Many of the problems one would encounter when swapping in an lt1 are the same (needs headers, some clearancing, brackets), but it seems way easier than a ls1 swap. You can use the stock mounts, the cooling system from the 4th gen, the Bell housing pattern is the same...
Is it a price thing? Mercruiser engine cores are like $300 out here. Maybe CT has very strict emissions restrictions on boats, even more than cars? Prices for BBC parts are WAY cheaper than lt1 parts, or even sbc parts out here.
Is it a mechanical thing? Do they not make a compatible Flywheel or something?
Help me out people, I've never heard a ThirdGen member say, "you know what you need? A smaller engine."

 

350 = SBC (Small Block Chevy)
383 = SBC
454 = BBC = BIG Block Chevy

Externally a 265=289=302=305=307=327=350=383. You can swap any of those engines into the same place... Same intake (mostly), same exhaust/headers, same motor mounts, same transmission. Yadda, Yadda.

The difference is the crank and pistons (and possibly rods). Same block, same heads. All the accessories, add-ons, bolt-ons, existing parts will work with either engine.

Once you switch to a BBC, whether 396, 427, 454, 496, heck a 596,
- you need new exhaust,
- valve cover interferes with wiper motor and/or brakes.
- it may not fit between the strut towers.
- it won't fit under the stock hood.
- beefier transmission
- rear axle = 9", 12 bolt or S60 = $2k and up. (Unless you know someone who knows somehow, or someone owes you a favor, etc)
- stiffer front springs to hold up the extra 100+ pounds.
- don't even think about the 366 or 427 (or aftermarket) tall deck blocks.

Of course, if you want to be different, want a big block, or are a big dog, you'll take all of these factors into consideration and do it anyway.

 

I would think you would need all those upgrades before a completely new engine anyways. Building a 383 using the stock exhaust, intake, rods, transmission, brakes, etc, sounds like a rookie mistake.
I think I understand what you're saying though: the idea of the 383 is appealing because it appears to be cheap. Especially with the number of go-fast magazine articles on the topic.
I'm more interested in the theory of it all though. It seems like it should be a very popular swap. Maybe we've been spoiled by the sheer number of bolt on parts available for the small block.

 

All good points. Staying with a SBC lets you have a "stock appearing" engine. A smog legal engine. Upgrade in phases.

 

This is definitely true, and a good point as well. But that doesn't seem to be a concern for most people not in California.
The "bolt on"/"upgrade in phases" theory seems more likely to me. But it is definitely hard to do well. The 1.5" primaries and 500 cfm Carb I have on my 305 are very nicely sized for a street vehicle, but would quickly strangle even a mild 350. Maybe with the 350 its an easier line to walk, but I don't know.
I think those magazines got us good. Back in the day I was set on building a fuel injected, turbocharged, 302. Nowadays, that stupid Goodwrench crate engine looks better all the time.
As for the Big Block thing, I think they're cheaper simply because they're less popular, for the same reason Vortec engines and t56 transmissions are so valuable now because we're starting to pick them clean. I sold an L31 block for like 4x what I payed for it. Those poor circle track guys are masochists, I swear.
As for the Mercruiser engines, I'm just trying to figure out what the next big thing will be. It seems like a really good and realistic combo.