Is anyone here knowledgable about Chevy small blocks?

So the F250 has a little brother, a 92 blazer.  It's going to be the daily with the wife and the camping rig, because the Ford is already way too far from stock comfort for her to enjoy.  It's at the shop right now getting a new engine put in since I live in an apartment now and can't swap it myself like I did with the truck.  I know this isn't a Chevy forum, but there isn't a place I trust more than you folks, so I figured I'd ask here since I got no answers on the gmt400 forum.

Using the stock 350 block, it's been rebuilt with a 383 kit and factory vortec heads.  The intake was changed as well to accommodate the heads and the swap from tbi to a 650 cfm avs2 carb.

Hydraulic Flat Tappet Camshaft & Lifters 1957-1985 Chevy 262-400
Part Number: 555-200104  
Lift: .465"/.465"
Adv. Duration: 282°/282°
RPM Range: 2200-5200

They're shooting for just 10:1 compression ratio too.  I'm expecting somewhere around 400 hp, nothing wild since it's not a high performance build and I made it clear driveability and low end power are what's important.  Does that seem like a reasonable expectation?  

I'm asking because the mechanic (who isn't the builder, that was offsite at a highly respected shop) claims he put the numbers in desktop dyno and expects 480 hp out of it.  I cannot see that being possible, that's 1.25 hp/ci which I don't see on a street engine on pump gas.  

I think they are being very optimistic with their HP estimate. That is a fairly mild camshaft, only 224 degrees @ .050 lift. Not roller either. Stock heads... presumably stock exhaust manifolds... basically a near-stock engine, aside from the cam and the extra 33 cubes.

HP is linked with RPM, and a camshaft that stops breathing in the low 5000s is not going to make a big HP number. Should be good at torque production though,  but my estimate of HP in that engine would be in the 330-350 range.

Even if the number he is quoting is flywheel hp with no accessory drive, it's still very inflated, IMO. You are right on to expect good low-end driveability with that combo.