built 406 or mild 350 w/whipple

A 406 with the Ramjet Intake and cam would be a TORQUE MONSTER. I'm talking the 395/Marine cam, that was used in the Ramjet 350s. It's not going to spin to the moon, but with the Vortec heads should be a solid driver, and have all the torque in the basement that you require.

 

Ring end gap too narrow for boost?

I'd set the Whipple aside for a mild 350. As already mentioned, you can't spin it fast enough for a 383 or 406.

[opening a can of worms]
As far as the whole SBC vs LS debate, repeat after me: "Power under the curve. Power under the curve. Power under the curve." ...and then apply that to what rpm band you're going to be driving in. He's already said "I rarely drive over 4500rpm". Give it up.

There's no way I'd do an LS swap for a tow vehicle. One of the comments was "Yes, I know that peak tq comes on earlier in the big block, but you're only going to notice that pulling max weight. Which if you were serious about, you'd have a diesel anyway...."

Wow, so we should either suffer with an LS motor that can't get the load moving from a stop, or buy a diesel that's twice the cost? No thanks, bruh. I'll stick with a well-built small block or a mild big block that is right in the middle of both capabilities.

 

Good point on ring gap. Commonly overlooked issue on aftermarket forced induction. Ask me how I know!
Diving into said can....
When I suggested that he consider an LS, he hadn't mentioned driving over 4500 rpm, so there's that. Also, yes, GM expects you to suffer with an LS or pay for a diesel. Not me, I literally don't care, I was simply making a suggestion, and then opining on what I consider unfounded info. Guess I touched a nerve in some folks. I own both types, there's a 5.3 in my daily, a 6.0 in my winter ride, and a 454 in my dually. All of them will and have towed loaded car trailers just fine. Just my experience.
Climbing out of the can now....

 

No worries. I just get tired of the "LS swap everything" crowd. If I were building a turbo'd race truck I'd jump on it. For every other use, I don't think they're the best option.

 

LS are sweet car engines. I've heard that with a 4" stroke crank (5.3L -> 383, 6.0L -> ~408?) They can make good torque. I haven't driven one of those.

Worth nothing is that the torque rating on a 6.0L is at 4200 RPM. A 350 vortec is rated at 2800 RPM. And the difference is 360 LB-Ft vs 330 LB-Ft. I honestly like my vortec better (granted, I have 4.10's and a 4L80 with .75:1 OD. I think the only LS 6.0 I've driven had 3.73's or worse).

For a truck:
Non-Emissions Diesel > Big Block Gas > SBC/LS stroker > SBC > LS

 

Doing a 400 these days I would go long rod, 5.7 inch/350 rods or so. Easier on the cylinder walls then the stock 400 rods.

 

Was feeling lil froggy the other day, put my foot into it in the ‘ol Tahoe. Even then it didn’t hit 5k n then hit the speed limiter. If I was strictly towing or hauling I’d have a Cummins, don’t want no stinking computer with one of those. But, don’t do that, tho would be fun, only thing haven’t built. Cam I’m prolly using is the extreme 268. I’ve used it before, sounds awesome and runs just as good. I figure it would make one nice motor...

 

OMG! you spun it to 5k? You need an LS! LOL kidding of course.

 

Somebody needs to up his game. My shift points are 5100.

 

Lol hey it’s got 205k on it, kinda impressed it did that n still had oil pressure. I love driving this thing, just want lil more to have some fun. Friggin killing me that I can’t start building the motor, funds just not there right now.